The hitter's feet must be completely located within the box. The hitter's feet may touch the sides of the box but cannot be out. In addition, the feet must stay inside when the hitter makes contact with the ball.
A player must step into the box within 10 seconds of the umpire telling her to enter. If not, the umpire issues a strike.
The player must keep at least one foot in the box between pitches, unless there is a foul tip, a time-out called, the pitcher or catcher is moving, there is an attempted play (such as the catcher trying to throw out a runner) or the ball is put into play.
Watch That Step
The hitter must never step in front of the catcher while the catcher is trying to give a signal, or the umpire may call the hitter out. In addition, the hitter cannot move in front of the catcher when a ball is about to be thrown.