[UmpJM]

Michael,

Here is the MLBUM reference that Bob J. mentioned:

REGULATIONS:

(a) The pitcher shall be charged with a balk if, while in contact with the rubber, he throws to the first baseman who is either in front of or behind first base and obviously not making an attempt at retiring the runner at first base. However, there is no violation if the pitcher throws the ball directly to first base in this situation.

Also note that there is no violation if the pitcher attempts a pickoff at second or third and throws to an infielder who is in front of or behind
either of those bases (i.e., this violation is only in reference to pick-offs at first base). Also see next paragraph in this section.

(b) There is no violation if a pitcher attempts a pick-off at second base and, seeing no fielder covering the bag, throws to the shortstop or second baseman, neither of whom is in the vicinity of the bag nor is making an actual attempt to retire the runner.

JM