I would think that the operative clause here is "in a seamanlike way"? 

Theoretically, if you're luffing a windward boat and neither of you have a spinnaker up, you can turn pretty quickly and it is still a businesslike affair, even if you come from running to close-hauled. A boat with a spinnaker up might not be able to go as fast as far before you cross from seamanlike to physically possible, but not seamanlike.

Practically though, leeward might be able to turn at about the same speed from 0 degrees to 90 degrees at about the same speed, since avoiding contact generally means you're keeping an eye on how fast the other boat is keeping up.

What is "seamanlike" when you have a spinnaker up and you cross 90 degrees is an interesting question... the match racing call seems to basically say it's all good to luff the spinnaker boat to HTW, as long as you're not so close that they can't drop the chute even if they wanted to...

Agree tough luck for W.  I'm sure most of us have been in a similar position to W.  No reason to penalize L.  W has to accept the risk being that close to L.  Given the original drawing, L was pointing slightly higher than W, W sailing slightly faster and closing the distance between the boats.  It would appear that if the L hadn't had the main sheet problem, W would have eventually passed L and become the leeward boat.

The following four Cases and Appeals define what is not appropriate.
 
WS Case 72 – Discussion of the word ‘flag’. (rule 60.2(a)(1))

RYA Case 2001/13 – A glove cannot be a protest flag. When the display of a protest flag is required but not complied with, a protestee’s objection at the start of a hearing to the validity of the protest is to be upheld even if the protestee must have been well aware of the intention to protest. (rule 60.2(a)(1))

US Appeal 66 – A 2-inch by 8-inch protest flag on a 40-foot boat is not of sufficient size or of suitable proportions to be “conspicuously displayed.” (rule 60.2(a)(1))

Sail Canada Appeal 63 – For boats greater in length than 6 metres, a protest flag must be perceived to be a flag. The flag must be displayed at the first reasonable opportunity. For a fully-crewed boat, compelling evidence would be required to justify display within minutes, rather than seconds of an incident. Failure to meet these requirements will render a protest invalid. (rule 60.2(a)(1))

Thanks so much, Mark. It's good to have these when racing outside the US, in order to have more credibility. 

Thank you Paul for the change. And thank you all for the helpful suggestions.