Matt, 

I think this is what you're setting up:

1. While beating to windward, Boat A on starboard comes together with Boat B on port, overlapped to leeward of boat C.
2. Boat A ducks boat B and C,
3. Boat D is 10 hull lengths behind A and hears some spirited conversation. 
4. Boat D thinks Boat C compelled B to break rule 10 and protests C. 

I think this should go something like this:

Boat C comes to the hearing and states, "Why am I here? Neither A nor B said anything to me. Boat D had his flag up and told me he was protesting me the next time we were near each other, but I have no idea what he thinks I did. 

The PC calls A and B as witnesses. and finds that the "spirited conversation" was "Tack or cross"......"cross".

Conclusions:

Boat B on port kept clear of boat A on starboard and complied with RRS 10. 
Boat C did not compel Boat B to break a rule, nor did she break a rule. 

Decision

Protest Dismissed

if there is a hearing and we thought another boat broke a rule, and we not join hem in the hearing as a party if they can be identified? When damage or injury especially.
"Exoneration for her breach" could that not be an appropriate penalty?
Redress is a benefit to competitors not available in other sports, sometimes the rules fail but that does not mean there is great assistance to some sailors.

Thoughts of others please :
Windy conditions in a top level event with no qualification requirements. So, experts sailing among those with far less experience of the class.
High speed catamarans with very pointy bows.
Boat P contacts boat S at some speed and causes significant damage to boat S. Redress definitely available.
Boat P suffers little or no damage and retires.
But, does 43.1(a) over-rule Rule 14, which requires the ROW boat to retire because significant damage has been caused by the breach of Rule 14 ?

While one of my mentors has always said that sailing isn't 'fair', it's just our job to apply the rules as fairly as possible. The strictest application of Rule 14 in these cases always seems to me to be grossly unfair and not in the spirit of sportsmanship or fair play.
Discuss, please.

Rule 14 does not require the right-of-way boat to retire because significant damage has been caused by the breach of Rule 14. Rule 14 requires the right-of-way boat to act to avoid contact when it is clear that the other boat is not keeping clear or giving room or mark-room. At that moment it may not be possible for the right-of-way boat to avoid contact. See Case 87.

I agree 14 does not require you to retire. You cannot however take a turns penalty if there is serious damage.

The scenario I was envisioning is:

Two boats on starboard tack (Yellow and Blue) approaching the pin end (port) of the finish line. Yellow hits the mark, breaking rule 31, but claims Blue compelled her to hit the mark by breaking rules 11 and 18.2(a)(1) and is therefore exonerated by 43.1(b).  Blue does not take a penalty or retire.

A third boat (Green) witnesses the incident and protests Yellow for breaking rule 31.

Is Yellow required to protest Blue in order to defend herself from Green's protest?

Hi Matt. I don’t think that a protest is required but it does seem wrong.  

There are many reasons that a boat might not protest when they are fouled. 

My hope is that this is resolved going forward.  

A third party protest could win this protest and result in either boat being penalized. 

No it does not have to protest. Seeing another boat broke a rule may protest se 60.4(c) (2) and the matter would be resolved this way.

Matt .. this is a great topic, as it offers several things to discuss and folk to realize.

I'm going to steal my own punchline and give the answer up front .. 

YES . a boat that is compelled to break a rule, as a result of another boat breaking a rule, even though the "compelled boat" is exonerated under 43.1(a) .. SHE SHOULD ALWAYS PROTEST THAT OTHER BOAT.

Here are some of the insights about the rule and some of my 'reasons why' .. 

1) Before we get started, its good to recognize RRS 43.1(a) requires only that the boat compelling another to break a rule, is also breaking a rule, not that they are breaking a rule and are not exonerated themselves under some part of RRS 43.  So, the compelling boat might also "have a reason" themselves .. they might also be compelled or they might be sailing within room or mark-room they are entitled to when they broke that rule and therefore are also exonerated for breaking a rule.  Or .. maybe not.

This is important in pin-wheel roundings where the inside boat gets no room but it is the outside boat #5 that is the actual culprit (or maybe #3 or #4).  The inside boat is exonerated, and each boat in turn, but they each should protest the boat compelling them as they might not know who caused it all .. the outside boat or someone in the middle.

2) Why the above is important is the focus of your OP.  If this protest gets to a PC and the ultimate "culprit" is not a party to the hearing (because the exonerated boat did not protest their compelling boat), you are leaving it up to the whims of the PC.  This is because the rules state that a committee "may" protest a boat when it learns information (in a hearing of a valid protest) that a boat, not party to the hearing, may have broken one or more rules in the incident.

A PC might handle this a few ways .. 

The PC might decide to protest Blue. During the hearing the PC learns about Blue.  Maybe Yellow says she was compelled by Blue but Green states that Blue was more than 1/2 a BL away when she crossed their sterns.  Both Green and Yellow confirmed Blue's involvement in the incident.  The PC might decide to stop the hearing, protest Blue, reconvene and start the hearing over with Yellow, Green and Blue as parties.

The PC might decide to not protest Blue, but acknowledge Blue's involvement in the incident.  Maybe both Green and Yellow state that Blue was there, and either their testimony align showing Blue compelling Yellow or maybe Yellow and Green disagree whether Blue compelled Yellow.  

Now the PC will decide based only on Yellow and Green's evidence and there is a chance that they find:

The PC might decide that there was no Blue boat. Well .. then Yellow stands little chance of being exonerated.

So, if you do not protest the compelling boat, you leave a lot to the discretion of the PC.

We judges do not want to spend our life in the room.
You should be exonerated if someone protests you which is unlikely.
Sit back and let process happen, you will generally be very happy.
Do not protest!

I am in Angelo’s camp on this one. Green, in accordance with the Principles “Competitors in the sport of sailing are governed by a body of rules that they are expected to follow and enforce.” Seeing a boat break 31 and protesting that boat would be in accordance with the principles and as the boat that breaks 31 protesting the yellow boat saves time and helps constrain what the PC’s options are (and also following the principles of enforcing the rules) which then should combine the protests, take the PC then holds a hearing, takes testimony and resolve the protest based on the evidence from the hearing.  They would need only to find facts that support the conclusions of 1. Yellow touched a mark/did not touch a mark and broke 31.   2. That blue kept clear/did not keep clear of yellow and broke/ did not break 11 and 18.2. 
3. Blue compelled/did not compel yellow to touch the mark. 

Results.  No rule was broken 

Or blue broke 11 and or 18.2 and is dsq, yellow broke 31 and is exonerated 

Or blue broke 11and/or 18.2 and is dsq (case where yellow didn’t touch the mark)

Why if ypu believe you are exonerated would you want to protest and risk putting your finishing position the the hands of an outside party the jury.?

Hi Michael.  That is indeed the rub. One of our challenges is the self policing of our sport.  It’s a blessing and a curse. 

By not protesting, you are advantaging the offending boat in relation to not only your position but the position of all the other competitors that did not break a rule in that race.  I do think there is a fundamental unfairness in that.  
The boat that broke the rule has an obligation to protest the other boat if they saw them break a rule.  If they do not because they assumed exoneration due to their foul are they not violation the Basic Principles. 

I’m conflicted here and I don’t really know the “right” answer.  

Rick

When i sit at the windward mark watching collisions with the mark,  i see no appetite for competitors protesting.
The fundamental rule refers to the fundamental principle of sportsmanship when not exonerated to take a penalty. 
Ws chose not to say to prorest when you see an infringement. 

I agree completely Michael.  It seems to me that is a problem with our game.  It’s a huge barrier to entry for newer sailors.  The idea that the rules are not being followed is scary.  I’d like to figure out a way to keep the Corinthian spirit of the sport and promote fair sailing.  

“Competitor enforcement of the rules is the tradition in our sport, and when the rules are not followed, we owe it to ourselves and our fellow competitors, for the quality of racing, to protest.”

Bill Ficker, skipper of INTREPID in the 1970 Cup defense against GRETEL II, National Sailing Hall of Fame

I can understand the skipper of a match racing boat talking of enforcing the rules. That is how they may win races. Is it so simple with say 80 boat fleets?

Mike re: "Is it so simple with say 80 boat fleets?"

Mike, in a match race, you have umpire boats trailing and applying penalties.

In a fleet race, each competitor is the rule-enforcement-eyes for the rest of the fleet.   Unless there is OTW judging, that's all we have in fleet racing.   

We must rely upon boats to "follow and enforce" the rules as they are called-upon and "expected" to do. 

A competitor can only control the interactions they are involved in or see but if everyone holds the fleet and themselves to a high standard we will all be better off.