KO redirects here. For other uses, see Ko. For other uses of knockout, see Knockout . A knockout (also referred to as a K.O.) is a winning criterion in several full-contact combat sports, such as boxing, kickboxing, Muay Thai, mixed martial arts and others sports involving striking. A knockout is usually awarded when one participant is unable to rise from the canvas within a specified period of time, typically because of fatigue, injury (serious or temporarily incapacitating, e.g. a bleeding cut above the eye can blind a fighter), loss of balance, or unconsciousness. A technical knockout (also referred to as a T.K.O.) is often declared when the referee or other judges (such as official ring physician, the fighter himself, or the fighter's cornermen) decide that a fighter cannot continue the match, even though he did not fail the count.Sugar, Bert.