Đo ván

Also known as KO, K.O.

right|200px|thumb|Ingemar Johansson knocks [[Floyd Patterson out, becoming boxing heavyweight champion of the world, on June 26, 1959.]] right|200px|thumb|A heavy blow to the head is a frequent cause of a knockout. Muhammad Ali delivers one to [[Brian London and retains his heavyweight championship by third-round KO on August 6, 1966.]] A knockout (abbreviated to 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, some forms of taekwondo and other sports involving striking, as well as fightin