Hunting and Trapping in Fleet Racing -- Q&A 2013 034

ISAF recently published Q&A 2013 034, and I think they got it wrong.

The question (which is a little hard to find in the Q&A) is, essentially:

If a boat A acquires right of way or changes course in such a way that a keep-clear boat B momentarily cannot keep clear, and then A immediately acts to give B room to keep clear, should one or both boats be penalized?

The answer they give is, essentially:

Not unless there was contact or B had to maneuver in an unseamanlike way.

This brings fleet racing in line with match and team racing, where there are calls saying that if a right-of-way boat ultimately gives the other boat room to keep clear and there's no contact, then the incident should be green-flagged (no penalty). These calls, and the Q&A, say, in effect, “No harm, no foul.”

Or maybe more accurately, “All's well that ends well.”

This basic idea has been around in match and team racing for a number of years. As an active match and team race umpire, I understand the motivation for this Q&A, and maybe even like it in some circumstances, because a “no harm, no foul” attitude reduces needless protests for situations where, ultimately, nothing happened.

Consider, for example, two boats maneuvering two minutes before the start. A and B are headed off to the right, beyond the race committee boat, with A two boatlengths to leeward and bows-even with B. A decides to go back to the line, so she luffs and tacks, with her helm hard over. At the moment she completes her tack, if she were to center her helm and go straight she'd run smack into B's starboard quarter; but of course, she doesn't do that. She keeps her helm over and ends up on a reciprocal course to B. Boat B never changes course, because she knows that A is simply “going back” and will get out of this situation with no harm to either boat; and in my experience B never protests. This kind of situation happens all the time, and Q&A 2013 034 says it's OK – even if B were to protest, the protest should be disallowed; and that's a good thing.

My problem is, whether this is a good idea or not, you can't get to the Q&A's conclusion from the rules. In other words, I understand the theorem – I just don't understand the proof.

The Q&A poses 4 incidents. Each of the situations is a little different from the other, and although the Q&A takes them all on at once, we'll look at them one at a time. Let's take the first scenario:

The situation 1 description, from the Q&A, is as follows:

A tacks onto starboard tack so close to B on port tack that A cannot sail straight ahead without hitting B, and B cannot avoid a collision by maneuvering promptly in a seamanlike way. A then immediately changes course to give B room to keep clear. A protests B under rule 10 and B protests A under rule 15.
 
Note the words, “A … changes course to give B room to keep clear.” This seems to require that we know A's motives, which we don't. Just above this statement, the description says, “A cannot sail straight ahead without hitting B”, so why doesn't the subsequent phrase say, “A … changes course to avoid hitting B”, which is clearly true, regardless of any other motives?

The answer is, if they had said that, then one of the boats would have to be penalized, because of the definition of Keep Clear:

A boat keeps clear of a right-of-way boat 

     (a) if the right-of-way boat can sail her course with no need to take avoiding action and,

     (b) when the boats are overlapped, if the right-of-way boat can also change course in both
          directions without immediately making contact.

The Q&A quotes part (a) of this definition, which is clearly the applicable part in situation 1.

It seems to me that, according to both the diagram and the description, if A had held her course at position 2 she would have hit B. So A needed to take avoiding action at position 2. So B broke rule 10 at that point, and A broke rule 15 by not initially giving B room to keep clear. It was A's breach of rule 15 that compelled B to break rule 10, so penalize A and exonerate B (see rule 64.1(a)).

In situation 2, B on port tack is clearly crossing A on starboard tack. After B commits to crossing ahead of A, A dials up on B to a point where B is no longer keeping clear. A then immediately changes course to give B room to keep clear. A protests B under rule 10 and B protests A under rule 16.1. According to the Q&A, neither boat should be penalized. The diagram is below.


Putting aside the difficulty of getting to the Q&A's answer from the rules, this situation raises some other issues. In situation 1, B sees A's maneuver and is able to eventually keep clear. But in situation 2, B has committed to the cross before A hunts up at her, so B is like a deer caught in the headlights. (The match-race Call where the keep-clear boat is unable to respond to a course change by the right of way boat is commonly referred to as the "Bambi call".)  At position 2, B reasonably thinks she's going to be T-boned and there's nothing she can do about it. If her skipper isn't scared out of his mind, he should be.

In match racing, where boats are not required to take penalties for breaking rules and we couldn't care less about terrorizing competitors, A's behavior doesn't cause a problem. But in fleet racing, and even in team racing, where all of “Sportsmanship and the Rules” is in effect, it causes a big problem, at least for me. What B sees is that she didn't make the cross, and A had to bear off sharply to avoid her. B is not in a good position to judge A's course because her perspective is constantly changing, so she may well not be aware that A hunted up on her; and A's protest reinforces the assumption that A's bear-off was to avoid hitting B. By hunting up and then bearing off sharply, A is perpetrating a fraud in an effort to draw a foul. She hopes that B will take to heart her duties under “Sportsmanship and the Rules”, and take a penalty. In other words, A wants to punish B for being sportsmanlike. To my mind, whether or not either boat breaks a rule of Part 2, A's behavior here breaks rule 2, and the Q&A Panel should be ashamed of putting this situation in the Q&A.

Situation 3 raises yet another problem. In that situation, A establishes an overlap from clear astern on B. The overlap is so close to B that A cannot change course in both directions without making immediate contact with B. A then immediately changes course to give B room to keep clear. A protests B under rule 11 and B protests A under rule 15.
Here, part (b) of the definition Keep Clear comes into play. At position 2, according to the Q&A description and diagram, A cannot change course in both directions (in particular, she cannot luff up) without immediately making contact with B, so B fails to keep clear.

The interesting thing here is that rule 15 says, “When a boat acquires right of way, she shall initially give the other boat room to keep clear, unless she acquires right of way because of the other boat’s actions [emphasis added].” What could be more “initially” than the situation in position 2, where A has just established the leeward overlap? Rule 15 says nothing about “ultimately” or even “a little later”; so how does the Q&A Panel get around this word?

Situation 4 raises yet another issue. A and B are overlapped, with B as the windward boat. A luffs quickly, and before B can move away from A in a seamanlike way, the boats are so close that A cannot sail straight ahead without hitting B. A then immediately changes course, giving B room to keep clear. A protests B under rule 11 and B protests A under rule 16.1.

Unlike the other situations, this scenario frequently occurs in fleet racing, and not uncommonly results in protests. It's also one of the main scenarios the rules-writers were thinking of when we wrote rule 16.1 in the first place, back in the 90's. Rule 16.1 was a huge game change; the old rules said that A could “luff as she pleases”. When we wrote rule 16.1 we fully expected that if B could show that A luffed too fast for her to react, A would be disqualified under that rule. And now the Q&A Panel is saying, “Not so. As long as there's no contact, let A play her nasty little games.”

Which brings us to the final interesting feature of the Q&A. What does contact have to do with this issue? There's no mention of contact in any of the rules involved here (rules 10, 11, 15 and 16.1), and the only mention of the word “contact” in the definition of Keep Clear clearly deals with an event in the future. In other words, when there's contact, the keep-clear boat was already breaking a right-of-way rule before that contact. ISAF Case 88 says, “‘Keep clear’ means something more than ‘avoid contact’; otherwise the rule would contain those or similar words,” and of course, that Case is right. It doesn't really matter whether there is contact; if the right-of-way needs to take avoiding action or cannot change course in both directions without making contact, then the other boat is failing to keep clear.

All in all, I think the Q&A Panel got it wrong, this time.

Correction to 'More about Redress'

In my last posting, I said about the second Farah Hall prescription, "Basically, it allows a disgruntled loser from a protest hearing to demand a new hearing, ..." This is not true.  Rule 62.1(a) allows requests for redress for improper actions by protest committees, but adds: "but not by a protest committee decision when the boat was a party to the hearing." So the disgruntled sailor has to be from a boat that was not party to the hearing.  This still allows a boat to take two bites from the apple if she wasn't a party to the original hearing, but at least she can't take a third and fourth bite.

I apologize for the error.

More About Redress

Since my last post on the subject of redress, I’ve received several comments from people I’ve met at regattas, agreeing with me that we should get rid of redress. Maybe there’s more support for this idea than I thought, though of course people who think I’m crazy probably don’t bring it up. If you think we should get rid of redress and be like every other sport in simply accepting unlucky breaks, let people know about it!

In the last post I covered the most common reason for requesting redress – actions or non-actions by race committees, protest committees, organizing authorities, and the like. 

In this post we’ll look at the other reasons a boat might request redress. 
 
Rule 62.1 (b)-(d) says a boat may request redress because of:

     (b) injury or physical damage because of the action of a boat that was breaking a rule
           of   Part 2 or of a vessel not racing that was required to keep clear;

     (c) giving help (except to herself or her crew) in compliance with rule 1.1; or 

     (d) an action of a boat, or a member of her crew, that resulted in a penalty under 
           rule 2 or a penalty or warning under rule 69.2(c).
 
Like the rest of rule 62.1, part (b) seems fair on the face of it; but not so fast. The problem with fairness here is that boats that are fouled in such a way that they lose a huge number of places are not eligible for redress unless there was damage, whereas boats that are damaged in perhaps insignificant ways can claim the damage was what hurt their finishing position, and get redress. Rule 62.1(b) does not require that the damage be substantial, the way rules 44.1(b) (taking a penalty) or 60.3(a) (protest committee hearing a protest that would have otherwise been invalid) do. 
 
On the other hand, rule 62.1 requires that the boat’s score was made significantly worse by the damage itself, not just by the incident. So if boat port-tacks you just after the start and puts a hole in your side and it takes 2 minutes to get the boats apart, can you claim redress for that delay? Reading the rule carefully, I'd say not; but I'll bet most protest committees would say otherwise. If the damage keeps you from sailing on starboard tack until you can duct-tape the hole shut, that’s clearly redressable. 

Rule 62.1(c) and (d) are the most defensible part of the redress rule, but the situations these parts describe are so rare that most sailors can go their entire lives without the events listed in this rule even happening.
 
There's one other thing about redress we need to look at. Some years ago, US Sailing instituted the “Farah Hall” prescriptions, so called because they were pressed upon US Sailing by Farah Hall, who was prevented from being selected to the US Olympic Team because of an incident in the Olympic Trials for the 2008 Games (she subsequently windsurfed her way onto the team for the 2012 Games). One of the Farah Hall prescriptions, to rule 60, deals with redress. It says, 
 

US Sailing prescribes that when redress has been requested or is to be considered, the protest committee shall make a reasonable attempt to notify all boats of the time and place of the hearing and the nature of the request or the grounds for considering redress. Before holding the hearing, the committee shall allow reasonable time for boats to make written requests to participate.

When we first wrote this prescription, I was of two minds about it – on the face of it the prescription seems fair, but it looked as if it could cause huge hassles for the protest committee. Suppose everybody in a big fleet decides to participate? The redress hearing could become unmanageable. But now that the prescription has been around for awhile and is in wide use across the country, I've changed my mind. The general experience I've heard about is that usually almost nobody takes advantage of the opportunity to attend the hearing, and even if lots of people show up for the hearing, a good protest committee can control the process so it doesn’t get out of hand.

The reason I like the prescription is that hearings are essentially adversarial processes, with the protest committee hearing both sides of the argument and deciding the outcome. For example, when there's a protest both the protestor and protestee are parties to the hearing, so both sides of the incident are presented. I can't tell you how many times I've thought the protestor had an open and shut case after she presented her side, only to discover that the protestee's presentation and witnesses cast the entire incident in a different light.

In the case of redress hearings, without the prescription above, usually the only person in the room who stands to gain or lose by the decision is the applicant. It's true that when the redress is brought under rule 62.1(a), the race officer or whoever is claimed to have done an improper act is a party, but nobody really speaks for all those boats that, if the redress is granted, will have lower scores for the event. In the case of requests for redress under rules 61.(b)-(d), there's nobody in the room to say, "Wait a minute.  That kind of damage doesn't really hurt a boat of this type,"  or "I saw them pick up the crew member that had fallen off her boat.  I punched my stopwatch and it was 3-1/2 minutes before she was returned to her original boat, not the 10 minutes claimed by the boat requesting redress."
 
So it makes sense to alert all boats about the redress request and the reasons given in it (usually, by simply posting a copy of the request on the Official Notice Board), so that anybody who may be hurt by the decision can oppose the request. 
 
The only really onerous effect of this prescription is to delay the hearing, and I think that can be taken care of through shorter protest time limits (or maybe a separate, shorter time limit for redress requests) accompanied by electronic communication of the required notice and the requests to be present. 
 
I don't have the same good feeling about the second Farah Hall redress prescription, which is to rule 63.4:

(b) [when practicable] a request for redress based on a protest committee decision shall be heard by a committee that contains no members of the committee that made the original decision.

Personally, I think this prescription is nuts. Basically, it allows a disgruntled loser from a protest hearing to demand a new hearing, and Rule 63.1 requires that once the request if submitted, there has to be a hearing. If there are any judges in the area who weren't on the original protest committee, a new committee must be formed that has no overlapping membership with the old one. And if the request for redress is worded cleverly, the new committee must essentially conduct an entirely new hearing. This gives the loser a “second bite of the apple”, which is distinctly unfair. In my opinion, if the sore loser really believes there were errors or the protest committee simply got the rules wrong, she can appeal. 
 

In cases where new evidence becomes available or the protest committee realizes that they have made a serious error, the loser of the original protest hearing or the protest committee itself can ask that the hearing be reopened so that the new evidence can be heard or the decision can be rethought. In such cases, rule 66 specifies that the panel for the rehearing have a majority of members from the original protest committee – exactly the opposite of the Farah Hall requirement. 
 

Note that the Farah Hall prescriptions can be written out, either individually or in toto, by the sailing instructions. I understand that there are entire areas of the country where it is the custom to do so. But I suggest that before you do this, you should put some careful thought into the value of these prescriptions, not just into the negatives – and I urge you to keep the prescription to rule 60. 
 

Alternatively, you could simply write out redress, altogether. Rule 62 is one of the rules that can be modified by sailing instructions (see rule 86.1). So organizers could simply put the following rule in their sailing instructions:

“SI n. Rule 62 is deleted.”

There might be people who love redress hearings and won't come to your event if they don't have an opportunity to file for redress, so you'd better include this change in the Notice of Race, too.

Redress

This posting is about redress.  Before we get into this topic, let me be clear – if I could, I’d remove redress from the rulebook altogether.  No other sport’s rules include the concept that somehow when things go bad on the field of play the results of the game or match or whatever should be set aside.   

The star player for a basketball team goes up for a shot and a player on the other team undercuts him.  He lands wrong and breaks his wrist.  There is a penalty against the other player, but that’s it.  Suppose after the game the injured player’s team were to  request “redress”, asking the league to erase the game and play it again after they’ve found another star to replace the injured player.  That would be crazy, right?  Yet that’s exactly what the Racing Rules of Sailing allow.  We should remove that provision from the rulebook and bring our sport in line with “real” sports, where competitors simply take bad luck, injuries and bad calls as part of life, and live with it.

But, like it or not, our rules do have a provision for redress.  Rule 62.1 says:

"A request for redress or a protest committee’s decision to consider redress shall be based on a claim or possibility that a boat’s score in a race or series has been or may be, through no fault of her own, made significantly worse by
    (a) an improper action or omission of the race committee, protest committee, organizing
         authority, equipment inspection committee or measurement committee for the event,
         but not by a protest committee decision when the boat was a party to the hearing;
    (b) injury or physical damage because of the action of a boat that was breaking a rule of
          Part 2 or of a vessel not racing that was required to keep clear;
    (c) giving help (except to herself or her crew) in compliance with rule 1.1; or
    (d) an action of a boat, or a member of her crew, that resulted in a penalty under rule 2 or
         a penalty or warning under rule 69.2(c)."

In this blog posting, we’ll look just at the first paragraph of rule 62.1 and subsection (a).  Subsections (b)-(d) will be considered in a separate posting.

The first interesting thing to note about rule 62.1 is that, technically speaking, it only limits the grounds that can be stated in the written request for redress, not the grounds the protest committee can use to grant it; but in practice, this rule serves to limit both the request and the decision.

The one exception is the words “claim or possibility”, which apply only to the request for redress, not to the decision – for the latter, we need to refer to rule 63.1, which says in part: “… A decision on redress shall not be made without a hearing,” and rule 63.6, which says: “The protest committee shall take the evidence of the parties present at the hearing and of their witnesses and other evidence it considers necessary. … The committee shall then find the facts and base its decision on them.” These rules imply that the protest committee cannot grant redress based on a claim or possibility, but only on facts found in a hearing.  After finding facts, the protest committee must decide if it is likely that the boat's race or series score was or will be made significantly worse.  If so, and the facts support the other requirements of rule 62.1, they should grant redress. 

Let’s look at those other requirements for redress.  First, a boat’s score in the race or series must be made “significantly worse” by the circumstance cited in the request.   I’m not sure exactly what “significantly” means in this context, but presumably a drop from position 43 to position 44 in a 100-boat fleet is not “significant” while a drop from first to second is.  There’s bound to be a wide range of interpretation of the word “significant”, but it’s almost a moot point.  If the effect is marginally significant then the action of the protest committee to grant the redress will produce a marginal change in scores and so is of marginal interest to the competitors.  To my mind, that word is not problematic. 

The expression “has been or may be” is new in 2013.  In the past, a boat could only apply for redress for something that affected the boat’s position in a race or races already sailed.  This is a welcome change, as it allows competitors to identify problems in advance of the competition and get them fixed, before they do their damage. 

For an example of this, suppose the NOR says that the competition will be held without spinnakers, but the SIs make no such provision.  A boat that based her attendance at the event in part on the fact that spinnakers would not be used asks the race committee whether spinnakers will be allowed and they say, yes.  She then requests redress, and the protest committee decides that the fairest resolution to the conflict between the NOR and SIs is to use the rule in the NOR banning the use of spinnakers.   Before 2013 that protest committee would have had to deny this boat’s request until after the first day of racing, and then abandon all those races.  Clearly it’s better to resolve the conflict before the event begins, and that’s what the new rule allows.

Rule 62.1(a) is by far the most common reason boats apply for redress, at least for non-kiteboarding events.  These requests are based on the allegation of an improper act or omission by one of the listed individuals or committees.  For simplicity of presentation, I’ll assume below that the race committee is cited in the request; the same principles apply to organizing authorities, measurers and so forth.

“Improper” is a very strong term.  To me, this word means redress for an action or inaction by the race committee can be granted in only two cases:  either the race committee broke a rule, or they made a decision that patently and intentionally favored certain boats over others.  It doesn’t mean a race committee decision that was within the rules but with which both the boat requesting redress and the protest committee disagree.  Such decisions might be wrong, but they’re not “improper”.

Suppose for example there’s very light wind.  The leaders are at a dead stop, a few hundred meters from the finishing line, when the race committee decides it’s unlikely that any boat will finish within the time limit for that race, so they abandon the race in accordance with rule 32.2.  Just after the abandonment signal a breeze fills in and it is clear that the first boat would have finished within the time limit if the race hadn’t been abandoned.  If the lead boat were to apply for redress because of the committee’s decision, they should not receive it because the race committee broke no rule and therefore their action was not “improper” – just wrong.

Suppose, on the other hand, that the race committee, seeing a local sailor leading the race, decides to shorten the race at the next mark, claiming it was unlikely that any boat would finish in time but actually because they wanted that local sailor to win and it was unlikely she would do so if the race continued.  That decision would be "improper" because it was made with the intent of favoring a particular sailor.  It's not enough, in my mind, that the decision is unfair; to be "improper" it has to be intentionally unfair. 

As another example, the RC signals an individual recall, then a few seconds later removes that signal even though one of the boats over early has not returned.  That action is “improper” because rule 29.1 says, “[the] flag shall be displayed until all such boats have sailed completely to the pre-start side of the starting line …” and the RC broke that rule.  If a boat was over early then decided not to return to the start based on the RC’s action, and she gets scored OCS, redress should be considered.

The next hurdle is “through no fault of her own.”  This is perhaps the toughest call.  In the last example, the boat requesting redress was over the starting line at the starting signal, maybe by a long way.  So, isn’t it partly her fault that she got scored OCS?  My feeling is that yes, it’s her fault that she was over the line at the start but it’s not her fault that she didn’t go back.  My principle here is that a boat is never at fault when she trusts the race committee.  By dropping the individual recall signal, the RC told her she wasn’t over the line at the start; she has a right to rely on that information in the face of any information she has to the contrary. 

ISAF Case 31 is a little muddy on this issue.  The situation there was an individual recall without the required sound signal.  A boat that was OCS but didn’t return to start was granted redress.  On the subject of “no fault of her own”, the Case notes, “Here, [the boat requesting redress] had no part in causing the race committee to omit the sound signal ... ,”  but then goes on to say, “… a boat that realizes that she was on the course side of the line is not entitled to redress, and she must comply with rules 28.1 and, if it applies, rule 30.1. If she fails to do so, she breaks those rules. In addition, she fails to comply with the Basic Principle, Sportsmanship and the Rules, and breaks rule 2 [Fair Sailing].” 

Holy moly, rule 2, the rule about unsportsmanlike behavior!  So, how about if a boat wasn’t OCS but thought she was; does she break rule 2 if she doesn't go back?  If not, why not?  Do the people who write these cases remember what it was like to “pull the trigger” at the start and then look back at the RC boat to see if they were over early?  I’ve had plenty of experiences when I thought I was over, only to find out I was wrong.  Good thing I didn’t remember Case 21. 

So, despite Case 21, I’m sticking to my guns – if the RC tells me I’m OK, I’m OK.

I think that protest committees should generally regard “fault” of competitors the way they should view “improper” when it comes to race committees – very narrowly.  In the example above, it’s true that the boat’s OCS score was partly her fault – but it’s not her fault that she didn’t go back.  To determine if her score was made significantly worse the protest committee should not compare the OCS score she received with the bullet she got in that race, but with her probable position in the race had she gone back.  

At an event I attended recently, the start time for the first race on the last day of the event was moved from 09:00 to 08:30.  This was a world-class event, with a press conference at the end of racing each day, that all skippers were required to attend.  The change in schedule was announced at the press conference but not posted on the official notice board, despite a sailing instruction saying all such changes would be posted before a certain hour the day before they took effect.  One boat showed up for the 09:00 start, only to find the first race in progress.  She was scored DNS for that race, and when she came ashore she requested redress.  The protest committee agreed that moving the starting time without posting the change was improper, but decided that the boat's late turn-out was partly her own fault, as she could have found out about the change in plan had her skipper listened better at the press conference.

In my opinion, that decision was wrong.  It was not her fault that the race committee failed to post the change, and it is never a boat's fault to trust the race committee.  Attendance, not attention, was required.  The boat should have received redress.

In a future post we’ll take up the remaining reasons for redress, as laid out in rules 62.1(b)-(d).

When does rule 18 turn off?

A question I hear often is "When does rule 18 turn off?"  At the simplest level, the answer is given by rule 18.1:

18.1 When Rule 18 Applies
        Rule 18 applies between boats when they are required to leave a mark on the same side and at
        least  one of them is in the zone.
        However, it does not apply
             (a) between boats on opposite tacks on a beat to windward,
             (b) between boats on opposite tacks when the proper course at the mark for one but
                   not both of them is to tack,
             (c) between a boat approaching a mark and one leaving it, or
             (d) if the mark is a continuing obstruction, in which case rule 19 applies.

If rule 18 does apply at some point during a mark rounding, part (d) clearly never applied.  Condition (b) is really just an extension of (a) for situations where there might be disagreement about whether boats are on a beat to windward, so we get the following summary: "Rule 18 turns off when either boat tacks at a mark to be rounded on its windward side, and when the leading boat leaves the mark while the other boat is still approaching it."

However, that's not the whole story.  The real question is, "When does the obligation to give mark-room end?"  And while that seems like the first question, it's actually quite different.  Basically, the obligation to give mark-room ends when the boat entitled to mark-room no longer needs it to pass or round the mark. 

Consider ISAF Q&A 2013-017.The animation at the left was used to draw the scenario in that Q&A; it shows two catamarans rounding a port-rounding offset mark, with the next leg directly downwind, in 10-12 knots of wind, no current.  At position 4 Yellow has passed the mark and both boats are on their downwind courses (which, they being catamarans, is not straight downwind).  Yellow jibes directly in front of Blue, breaking rule 10 (Port/Starboard).

Blue is required to give Yellow mark-room at this mark because Yellow is clear ahead at the zone.  According to the definition Mark-room, Blue has to give Yellow three things:

1. Room to sail to the mark if her proper course is close to it;
2. Room to round the mark as required to sail the course; and
3. Room to leave the mark on its required side.

(I've changed the order of the requirements in the definition Mark-room so that they appear in time order, making them easier to discuss here.)

Consider the situation at position 4 of the animation.   Yellow's proper course is no longer close to the mark, so she no longer has the right to room to sail to it.  She is on her downwind starboard-tack course, so she has rounded the mark as required to sail the course.  And Blue has clearly given her room to leave the mark on its required side. Thus, Blue's obligation to give Yellow mark-room has been discharged and she is no longer obliged to do so.

That conclusion is particularly important because of rule 18.2(c)(2), which says:

(c) When a boat is required to give mark-room by rule 18.2(b),
      (1) she shall continue to do so even if later an overlap is broken or a new overlap begins;
      (2) if she becomes overlapped inside the boat entitled to mark-room, she shall also give
            that boat room to sail her proper course while they remain overlapped.

At position 4, Blue has become overlapped inside Yellow.  But because Blue has discharged her obligation to give Yellow mark-room, she is no longer required to do so and the initial phrase in rule 18.2(c) does not apply to her.  Therefore rule 18.2(c)(2) does not apply.  Yellow's breach of rule 10 is not exonerated under rule 21 and she should do her turns.

 Now consider a situation at a port-rounding leeward mark, with the next leg a beam reach (as with Mark 3 in a standard digital-N course in team racing). Blue is overlapped when she enters the zone, so she is required to give Yellow mark-room.  By luffing Yellow at positions 3-4, does she break rule 18?

I think the answer is no.  Refer again to the list of requirements from the definition Mark-room.  Blue has certainly given Yellow room to sail to the mark, and just after position 3 Yellow is on her course to the next mark, so she has been given room to round it.  At position 4 Yellow  has not yet passed the mark on its required side, but Blue is not preventing her from doing so.  Thus unless Blue luffs Yellow into the mark she has given mark-room as defined and has no further obligations.  

Note that this isn't as clear-cut as the previous example because not all the conditions of the definition Mark-room have been met when Blue luffs Yellow above her course to the next mark: Blue still has to allow Yellow to leave the mark on its required side.   So one could argue that until all the parts of the definition have been met, Blue has no right to interfere with Yellow.  But I don't think that conclusion is supported by the wording of rule 18 and the definition Mark-room.

If I'm right, this has an interesting consequence for team-racing: it essentially allows the outside boat to set a "post-mark trap" at Mark 3.  Suppose Blue has a team-mate close astern; then this play allows that team-mate to pass while Blue holds up Yellow.  You might say, Blue could have accomplished this by luffing later, along the leg, and that may be true -- but it may not, because if Blue allows Yellow to trim in and reach along the next leg, she may lose any real opportunity to luff Yellow above close-hauled, which she needs to do if she wants to hold Yellow up.  It's only the presence of the mark that forced Yellow to come down into the vulnerable position she's in at position 4.