I can understand not letting the coach into your "private" space after the game, but who knows if that was also his team's storage room? I work a parochial school league (5th to 8th graders, boys and girls) where I sometimes don't even have a room to get away from the coaches, fans, etc. The best I've ever gotten out of any of these schools in that league is a storage closet that opens right out into the gym, and is accessed by each coach from that school. Sometimes it's unavoidable.

Best thing to do in a situation like this is to simply ask the coach to leave so that you have time to prepare for the next game.