Blue is on a collision course with Red and must keep clear in accordance with rule 10 (boats on opposite tacks). Just before the starting signal, Red changes course towards the starting line, at which point Blue is still able to keep clear by tacking, but Blue does not do so. Therefore Blue infringes rule 10 and will be penalized. Red does not infringe rules 16.1: Red is OK under 16.1 since her course change left Blue room to keep clear by tacking.