My partner called this play a balk and I disagree.
With runner at first and pitcher in the set position, the runner breaks for 2nd. The pitcher disengaged the rubber and threw to second base. Base umpire immediately called a balk. His reasoning was that the pitcher threw directly to an unoccupied base. my thoughts are that once he disengages he can throw anywhere and also once a runner breaks or even feints an attempt the pitcher can throw to that base as long as their was no motion to pitch home
Original Post