The batter steps out of the box and causes the pitcher to balk.
By rule, a batter can not cause a pitcher to balk. A balk is the result of an illegal action by the pitcher while any base is occupied. If the batter leaves the batter’s box with both feet during the pitch and the pitcher delivers the pitch, two strikes are called on the batter. If the pitcher doesn’t deliver the pitch there is no penalty for the batter or pitcher.