Question
Yellow, ahead of Blue, is taking a penalty around the finishing mark. As Yellow tacks and bears away on port, Blue, approaching the mark on starboard, bears away and gybes to port. There is a Y flag. What should the call be?

Answer
When Yellow passes head to wind, she begins taking a penalty and must keep clear under rule C2.8 until she completes her penalty by bearing away to a downwind course. In addition, rule 18.2(a) applies, since the boats are overlapped and about to pass the mark on the same required side. An alteration of course by Blue may be either to keep clear of Yellow, or to give Yellow room at the mark, or both. If Blue is required to alter course before Yellow completes her penalty, Yellow is not keeping clear under rule C2.8 even if Blue is altering course to give room.
Signal that Yellow has completed her penalty and penalize Yellow again for breaking rule C2.8. See Call MR 28.
If Blue’s alteration of course is not required until after Yellow completes her penalty, display the green and white flag.