Pitcher throwing to unoccupied base

[parrothead]

Had discussion about this one with very experienced ump, one of the key things to my question which he mentioned is the timing. So lets say the lefty move if the Lefty raises his leg then the runner breaks, he must continue with throw to 1st because otherwise move would be considered throwing to unoccupied base since the time of the first move by the P the runner was not advancing yet, he only started to advance after the pitcher lifted his leg. Same thing with RHP, if that left foot goes up, he cant "guess" the runner is stealing and turn to 2B, if he does its a balk, unless the runner breaks before the p lifts his leg, like an early steal.