My son plays, in my opinion.., solid and attack-oriented tennis when he is playing with confidence - that is, when he is not worrying about the possibility that he could miss the shot. He recently met an opponent who yelled YES! YES! regulary when my son double faulted or when he made an unforced error. My son started to focus more on not missing shots and less on winning points - and lost the match.. How should he counter this behavior? Turn the match into a yelling contest?