How would you decide this?

Dave Perry’s 100 Best Racing Rules Quizzes highlights specific aspects of the racing rules in a fun format designed to help you become more familiar with The Racing Rules of Sailing. Here is one of the quizzes:

Quiz 44
Boats SA and SB, two starboard-tack boats, are approaching the left-hand gate mark (looking downwind) to be left to port. When SB reaches the zone, SA is clear ahead of her and outside the zone. SA gybes, and SB gybes to round the mark in front of SA but loses control of the boat, and SA overlaps SB on the inside. SB regains control and luffs quickly to round the mark, making contact with SA with no damage or injury. Both boats protest. You are on the protest committee; how would you decide this? Answer below.

Quiz 44 answer
Boat SA is disqualified for breaking rule 18.2(a)(2), Giving Mark-Room.

When SB reached the zone, she and SA were not overlapped, and SA was not in the zone. Rule 18.2(a)(2) states: “if the boats are not overlapped, the boat that has not reached the zone at that moment shall give the other boat mark-room.” The rule continues: “When a boat is required to give mark-room by this rule, she shall continue to do so for as long as this rule applies, even if later an over- lap is broken or a new overlap begins.”

Boat SA was required to give Boat SB mark-room, which is the space SB needs to sail to and around the mark in a seamanlike way (see the definitions Mark-Room and Room). SA failed to do so, and therefore she broke rule 18.2(a)(2). SA also failed to keep clear as a windward boat under rule 11, On the Same Tack, Overlapped.

However, because SB changed course quickly and did not give SA room to keep clear under rule 16.1, Changing Course, SA is exonerated (freed from penalty) by rule 43.1(b), Exoneration, for her breach of rule 11. Because SB was sailing within the mark-room to which she was entitled, she is exonerated by rule 43.1(b) for her breach of rule 16.1.

SB could have avoided the contact, so she broke rule 14, Avoiding Contact. But because there was no damage or injury, she is exonerated by rule 43.1(c) for her breach of rule 14. SA could not have avoided the contact from the moment SB luffed, so she did not break rule 14.