Missouri and Kansas umpires allowed the lhp to throw to second if you broke on first movement from first. I argued it for three years that the pitcher could only throw to an occupied base but their explanation was that once he got 2/3 of the way to second it was considered occupied so by the time the ball got there it was occupied. I argued that the base had to be occupied when the play started but to no avail. Gotta love rule interpretation. That made it very hard to steal on a decent lefty.
It is like that all over the country - and not an interpretation. It is written very clearly. (Bold is my edit).
In fact, if a runner breaks on 1st move, the P can pivot to 2nd... feint the throw and then if disengaged from the rubber, throw to 1st if the runner is returning.
Another misunderstanding of the rules, that there are different rules for LHP and RHP. So even a RHP - when the runner breaks on 1st move can pivot and throw to second... even if unoccupied.
6:2:4:B
ART. 4 . . . Balk. If there is a runner or runners, any of the following acts by a pitcher while he is touching the pitcher’s plate is a balk:
b. failing to step with the non-pivot foot directly toward a base (occupied or unoccupied) when throwing or feinting there in an attempt to put out, or drive back a runner; or throwing or feinting to any unoccupied base when it is not an attempt to put out or drive back a runner;
If the coaches really studied the rules, there are a lot if small things that they can use to help give their players an edge.