Illegal Pitch – When is it enforced

I had a discussion with one of my senior base umpire between innings in a high school varsity game last week: Me: "Are you seeing a crow hop or leap by the pitcher" Base Umpire: "Yes, but the base coach has not said anything about it, and I'm not calling it until she says something"Where in the rules book does it say that we only call illegal pitches after an offensive coach has requested it?Is this a common practice in most associations? When playoffs or cross region tournaments begin, illegal pitches begin to be called. In my opinion, this is unfair to the young ladies who have been pitching a certain way all season, and now, when the games are the most important, we are calling these same pitching motions illegal.