I have a friend who was an Umpire in Chief for a local rec youth baseball league for several years. He always said the best rule he put in was, if a fan is unruly and gets ejected, that team's coach is also ejected. As an umpire, if a fan is getting out of hand, all they had to do was remind the coach that if the fan goes, he goes too. They never had any problems because the coaches would handle their fans.