Rule sets / OBR / Catcher Interference Balk
Catcher Interference Balk
Some instances of catcher's interference also carry a balk penalty.
If, with a runner on third base and trying to score by means of a squeeze play or a steal, the catcher or any other fielder steps on, or in front of home base without possession of the ball, or touches the batter or his bat, the pitcher shall be charged with a balk, the batter shall be awarded first base on the interference and the ball is dead.
MLB Umpire Development Manual Authoritative interpretation
Under Official Baseball Rule 6.01(g), if a runner is stealing home when the catcher interferes with the batter, the additional penalty of a balk is invoked, which enables all runners on base to advance (whether or not they were stealing). This can only occur when catcher's interference is enforced with a runner on third base attempting to steal home plate and a runner on second who remains at second base (not attempting to steal). In this case, the batter and runner from third base would be awarded third base for the balk penalty. Otherwise, in all other situations with a base(s) occupiped, all runners would be forced to advance when the interference is enforced.
Video examples
Bryce Harper attempts to steal home. The catcher interferes with the batter. When the balk is enforced, the runner from second base is awarded third base even though he was not stealing on the play.
Virginia Tech catcher is called for interference during an attempted steal of home. While this is a situation that an additional balk is enforced, the result is the same as the runner on first is forced to advance when the batter is awarded first base.