Rule 62.1b would cover that situation. It is not required that a boat file a protest on an incident in order to request redress.

62.1 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 or place in a race or series has been or may be, through no fault of her own, made significantly worse by

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

Mike, in these situations, I like to think about how the incident might get to the PC.
Your scenario helps make a few points:

• First, your scenario drives me to the Basic Principle (Sportsmanship and the Rules). The competitor has been given the primary responsibility to both follow and enforce the rules. This includes the responsibility to protest in cases such as this. Further, one of these guys was likely obliged to retire upon learning of the serious damage (RRS 44.1(b.))
• Second, RRS 60.3(a.) provides a PC the mechanism to initiate a protest, however, there are strict limitations under which such a protest may be validly lodged.
• Finally (and this is a personal POV), I am loathe to reach into these incidents as a PC if the competitors cannot be bothered to properly file their own protests/RfR. Having said that, I have occasionally seen situations where the damage was so great and injuries so extensive that we had to file a Request for Redress on behalf of a competitor who was unable.

So my question to you is: How would your incident have gotten to the PC?

Consult Case 142.

Furthermore, you were talking about proof of fault
If S request is valid, the protest Committee hears it and S has to show she fulfils the requirements of rule 62.1(b), in particular that P was required to keep clear, failed to do so and caused serious damage (in the incident or as a consequence). If S cannot prove it, S cannot be granted redress.
S can bring P as a witness in the redress hearing, or having other witnesses, make her case based on trackers and other physical evidence (video, damage).

S can protest P, but I believe that unless there is another penalty than retiring, for causing serious damage, the Protest Committee should either protest P or offer her the possibility to retire if she did not realise the damage before.

If S lodged only a request for redress and the Protest Committee does not write P as another party in this hearing on the hearing schedule, the Protest Committee will not hear any protest and cannot penalise P.
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As mentioned by Fields Gunsett, case deals rather deeply with this question.

Well said Grant.

Still on the matter of redress, what is the general opinion of judges regarding various proposals currently under consideration by WS to significantly revise, even delete, parts of the redress rules?

Phil.

I just want to comment on Phil's question. The answers on Mike's original question are all good and of course deal with it well . I think in practice in that situation, the boat on port, when she gets ashore, often realises what has happens and retires. If not she should be protested.
On the question of whether we allow too much redress, Phil and I have often had discussions. The argument in favour of reducing the right to redress is that in other sports people suffer and just lose out. I remember a case in an athletics race, when a girl (I forget her name, but she was South African and ran barefoot) was pushed into the inner line of the track and lost what probably would have been a gold medal.
There was a time when boats were much more delicate - wppd cracked, cotton tore, cotton ropes were weaker - and contact between boats really did cause unfair damage. The argument now is that if boats suffer because race officers make a mistake, or because of a contact, such as this example, the boat (and the helm and crew) should just put up with it and do better in the next race. I have a sympathy for that thinking.
I don't think there is any suggestion that a boat should not get redress if she goes to help someone in danger, of if she suffers from someone acting unfairly and thus breaking rule 2 or even rule 69.
I think any idea like this needs some testing before a change is made, but I think a test in a few regattas would be worth while.

....... back to my original question..... if S did not Protest, would P be cited as a witness at a Redress Hearing? How would the Committee proceed if the Witness did not attend the Hearing? Would it accept the unchallenged testimony of S?

I've just read case 142, which as Fields Gunsett says, deals with the issue.

Thankyou all.

Mike, I tried to put my fingers on a previous thread where this question was really thrashed-out (I had hoped to provide you a link to it, but didn't find it).

I can remember observing that examples (a) and (b) in Case 142 seem to be guiding that the "evidence" be in the form of an foul-acknowledgement of sorts (both examples given are of that type of evidence). That said, the way (c) is written, it's really left open to "any other evidence", which really swings the door wide open and begs the question of why guide so consistently with (a) and (b). In the end, (c) is pretty clear that it can be "any other evidence".

Sorry I couldn't find the thread. - Ang