The left-handed batter (B1) attempts two unsuccessful drag bunts (foul balls on each attempt). After the second attempt (with a 0-2 count) and before the ball is put back in play by the plate umpire, B1 moves from the left-handed batter's box to the right-handed batter's box.

 

The defensive coach reminds the umpire the once a batter takes a pitch as a left-handed batter, he must complete his at-bat as a left-handed batter (and certainly cannot change batter's boxes with two strikes).

 

What does the umpire do now?