[JR12]

Rule 606
A batter is out for illegal action when,
(c) He interferes with the catcher’s fielding or throwing by stepping out of the batter’s box or making any other movement that hinders the catcher’s play at home base. EXCEPTION: Batter is not out if any runner attempting to advance is put out, or if runner trying to score is called out for batter’s interference.
Rule 6.06(c) Comment: If the batter interferes with the catcher, the plate umpire shall call “interference.” The batter is out and the ball dead. No player may advance on such interference (offensive interference) and all runners must return to the last base that was, in the judgment of the umpire, legally touched at the time of the interference.
If, however, the catcher makes a play and the runner attempting to advance is put out, it is to be assumed there was no actual interference and that runner is out--not the batter. Any other runners on the base at the time may advance as the ruling is that there is no actual interference if a runner is retired. In that case play proceeds just as if no violation had been called.

So if batter moves into the catchers way, he interferes and the runner is not retired he's out. Batters should be taught to stand still and make the catcher throw in front or behind them.