Weird situation today. R1 on First. F2 in a full wind up but is positioned just behind the mound. He takes a step back with his pivot foot(right foot for right handed pitcher). He picks off the runner at first. This move is 100% legal if he is on the mound but would it be a balk since he was initially positioned in a full wind up just behind the mound?

Just behind the "mound?" I assume you mean behind the rubber.

If the pitcher made a pitching motion while he was on the rubber, this would be a balk. Just standing there is *probably* not a balk. Besides, if it was a balk, you would have called it way before the pick-off.

Is being behind the rubber in the windup position and then taking one step back with the pivot foot considered a pitching motion?(and thanks for your help with the illegal sub. I understand it completely now!)