Snappy Response?

[Loudwhistle2]

Called a shooting foul last night because a player grabbed the shooters bicep and prevented the shot from being released. Report foul, coach wants explanation of why we are shooting free throws. I tell him the shooter was in the habitual shooting motion when he was grabbed on the arm. Coach says, "but he never released the ball!" I say, " he doesn't have to, he only has to start his shooting motion." Coach says, "I've never heard that before!" I snap back, "check the rule book!" He sort of glares at me. I haven't ever said my last comment to a coach and its kind of bothering me, any suggestions on a better reply?