Doesn't the umpire have some discretion about the behavior of fans, though? At one of our games, the opposing team's bench cleared and they stood behind the backstop, directly behind the umpire and screamed. The umpire called time out, walked up to our pitcher, and told her if they were bothering/distracting (not sure exactly what the wording was) her, he would ask them to stop. (she said they were making her mad enough to pitcher harder, which she did, and of course that quited them down).
At another game, a parent from an oppsoing team consistently stood behind the backstop when we were in the field, shaking a can of coins or rocks or something that really made a racket and he screamed constantly. The umpire eventually told him to stop.