Bouts usually continue until one fighter is struck by an "incapacitating" blow or otherwise becomes disinclined to continue. A fighter may also yield (concede victory to the opponent) at any time during the bout. An "incapacitating" blow is defined as a valid attack to the head, neck, torso, armpit or inner groin area. Attacks to the legs or arms are considered "disabling". A hit to the arm disables that arm, which is held behind the fencer's back or hanging limply at their side. Fencers whose sword arm is disabled can switch hands. Some kingdoms use rules with additional details for strikes to the hand, which may simply disable the hand (represented by making a fist) or apply to the whole arm. For a strike to the leg or foot, the fencer can continue fighting but must kneel, sit on the ground, or balance on one leg. Under Cut and Thrust rules, hits to the leg or foot are considered incapacitating. Many kingdoms contain additional clarifications of these rules, such as only permitting sitting on the ground when the leg is hit, and/or limiting the permitted angle of approach for the opponent while seated (to avoid unsafe strikes to the back).