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 fighting-based video games. When a person is hit with a large amount of force to their head, it causes the head and neck to jolt in the direction that force is pushing it. This force then impacts on the movement of the brain. That same concept applies to the movement of a fighter's brain after they receive a knockout blow. But being on the losing end of a KO punch can damage a lot more than a pugilist's pride—research suggests that the blows that cause knockouts can be debilitating to a boxer's short and long-term health. Repeated blows to the brain can cause chronic damage such as personality changes and dementia. In most cases, a knockout lasts less than 10 seconds, after which the person regains consciousness. However, a bad knockout can last longer than a minute and even several minutes. The length of the knockout depends on the severity of the concussion and whether or not the brainstem was damaged. Top Knockouts. Best UFC knockouts, boxing knockouts, scariest knockouts, deserved knockouts, MMA knockouts, best knockouts street fights, heavyweight knockouts, worst knockouts, knockout king.