A knockout (KO or K.O.) is a fight-ending, winning criterion in several full-contact combat sports, such as boxing, kickboxing, Muay Thai, mixed martial arts, karate and other sports involving striking. A full knockout is considered any legal strike or combination thereof that renders an opponent unable to continue fighting.
The term is often associated with a sudden traumatic loss of consciousness caused by a physical blow. Single powerful blows to the head (particularly the jawline and temple) can produce a cerebral concussion or a carotid sinus reflex with syncope and cause a sudden, dramatic KO. Body blows, particularly the liver punch, can cause progressive, debilitating pain that can also result in a KO.
In boxing, kickboxing, etc. a knockout is usually awarded when one participant falls to the canvas and is unable to rise to his feet within a specified period of time, typically because of exhaustion, pain, disorientation, or unconsciousness. For example, if a boxer is knocked down and is unable to continue the fight within a ten second count, he is counted as having been knocked out and his opponent is awarded the KO victory.
In mixed martial arts (MMA) competitions, no time count is given after a knockdown, as the sport allows submission grappling as well as ground and pound. If a fighter loses consciousness (“goes limp”) as a result of legal strikes, or does not immediately defend himself after a knockdown, he is declared knocked out. As many MMA fights can take place on the mat rather than standing, it is possible to score a KO via ground and pound, a common victory for grapplers.