[AtlUmpSteve]

I don't think you are asking the right question. Illegal pitches can occur before a pitch begins; they occur at the time a pitcher violates the pitching rule (assuming the pitcher cannot and does not undo the violation by legally stepping off). As one example, a pitcher can violate by applying a foreign substance even during a dead ball.

At the same time, you (PU) can also effectively undo (or ignore) the first touches which may occur before the batter is set by holding your hand up to stop the pitcher. In that "no pitch" setting, you can safely ignore the technical violations that exist to protect the batter, since there is no batter. Remember, if the pitcher started pitching with your hand up, the result is "no pitch", so her motions or touches are either a "no pitch", or nothing. Once you drop your hand, the pitcher must then comply with the pitching rule, so a single touch is still appropriate, and required.

In the case of the pitcher stepping on with hands together, remember that the pitcher can still legally step back off before she separates.