A half swing at a pitch where the batter is able to stop the swing before they fully extend their wrist. If a batter "breaks" his wrist then it is a swing. If the catcher thinks that a batter did swing and the home plate umpire did not call a strike, the catcher will appeal to the first base umpire for a right handed batter or third base umpire for a left handed batter because they have a better angle to tell if the batter did swing.