illegal pitch or not

[drwells1]

O.K. guys here is the situation. I had already finished my games for the night and was watching an adult slow pitch game with stealing( after the ball reaches the plate). The pitcher was on the rubber and started her pitch and stumbled. She stopped her pitch and reset herself to do it again. At this time the plate umpire calls illegal pitch and moves the runner on first to second. I have never done this and never seen this done. I approached him (after the game) and asked him what was up with the call. He said that our association director told him in a previous game to start calling that way. We have no association rules about this Just wondering if this is the correct way to call any stop in motion by the pitcher?