The coach is very focused on football and on making football as violent as possible for the players. We could argue that he's villainous, because he lets other players attack Jerry on the field in a way that is totally unrelated to the game. But, his actions don't really drive the plot one way or the other. We think he's in the book to show how there's no area of Trinity without violence. Sure, football is a physically grueling sport, but the coach seems to disregard the rules that make the game a little safer for everybody.