I think it's important that the coach has a clear expectation of what will be called a strike or an illegal pitch. He may already have had a conversation with the League President.
My point is not to rub it in his face, but to clarify the rule. He's obviously mistaken or confused about this rule, perhaps things get blended together from a slow pitch league he might be involved in, I don't know.
Could be he'll walk up to me before the game and tell me everything is clear as a bell for him now. But if that doesn't happen, I'll clarify and set expectations. No sense going through a game that one team thinks I'm not doing something properly.
I'll call it a pre-emptive deflection.
Ted