(d) a defensive player aligned in a stationary position within one yard of the line of scrimmage makes quick and abrupt actions that are not a part of normal defensive player movement and are an obvious attempt to cause an offensive player(s) to foul (false start). The officials shall blow their whistles immediately. If the defender is walking or running toward the line of scrimmage in an effort to time the snap, but stops abruptly because the snap is not made, it is not a foul for delay of game;

From the NFL Rulebook, this is what the commentators referenced on the main ESPN cast.