A Knock Out, or K.O., is a term used in boxing games, fighting games and similar titles that denotes that one of the competitors has been rendered unconscious by the victor. In boxing, a K.O. is scored when one fighter falls to the mat after taking a pummeling and is unable to return to his or her feet within the span of ten seconds. This scoring method is commonly emulated in boxing video games such as Punch-Out!! and Fight Night. A knock out is also a common way of defeating the opponent in MMA and UFC games.
In fighting games such as Street Fighter II or Soul Calibur, a K.O. is rendered when one fighter deals enough damage to deplete his/her opponent's health meter. When a fighter's health meter is empty, the character is knocked out and the round ends. Unlike in a boxing title, where a fight ends when one of the competitors is knocked out, fighting games typically end after characters are knocked out multiple times; the most common match set-up in fighting games is to win two out of three rounds. In the event that two fighters manage to knock out each other simultaneously, the result is most often referred to as a Double K.O., in which case the round counts as a victory for both fighters.
Use of Knock Outs in Other Genres
Outside the scope of competitive fighting, Knock Outs may be tallied in games such as brawlers or action titles in which the player does not explicitly kill their enemies. For example, in the Dynasty Warriors series, the tally of enemies defeated in a stage is listed as the K.O. count rather than the kill count. This method of statistic labeling is generally used as a means to keep the intended rating of the game below the mature level.
In RPGs, party members that fall in battle but can be revived to continue on are typically given a status effect label to the effect of K.O. This is meant to indicate that though the character's hit points are at zero, he/she is not dead.
Stealth titles offer the player the opportunity to render enemies unconscious rather than kill them. Doing so has inherent risks, as enemies rendered unconscious will eventually awaken and continue to pose a threat. However, it may be a more preferable option than killing enemies and potentially leaving their corpses where other soldiers may find them and sound alerts. The Metal Gear Solid series often rewards players for using tranquilizing weapons to defeat bosses in exchange for in-game rewards.