Single-elimination tournament

A single-elimination tournament is a common method used to determine the champion in a wide variety of competitive, particularly, athletic, contests.

The term connotes the idea that one defeat eliminates the contestant or team from winning the championship or first prize in the event; it does not, however, always mean that the defeated competitor will not participate further in the tournament, as in many tournaments, consolation or "classification" contests are subsequently held among those already defeated to determine the awarding of lesser places.

Whenever possible, single-elimination tournaments consist of a number of participants which is a multiple of two, such as four, eight, 16, etc. (in tennis this number can go as high as 128). The competitors are then paired off, one round at a time, after which the number still eligible to win the championship is reduced by half. The round in which only eight remain at the start is generally called the quarterfinal round; this is followed by the semifinal round in which only four are left, the two winners of which then meet in the final or championship round.

When matches are held to determine places or prizes lower than first or second (the loser of the final-round match gaining the latter position), these typically include a match between the losers of the semifinal matches, the winner therein placing third and the loser fourth; sometimes contests are also held among the losers of the quarterfinal matches to determine fifth through eighth places (this is most commonly encountered in the Olympic Games). In the latter scenario, two "consolation semifinal" matches may be conducted, with the winners of these then facing off to determine fifth and sixth places and the losers playing for seventh and eighth; or some method of ranking the four quarterfinal losers might be employed and only one round of additional matches would be held, the two highest-ranked of the quartet then playing for fifth and sixth places and the two lowest for seventh and eighth.

In cases where the number of competitive entities at the start of the tournament is not a multiple of two, one or more competitors may receive a bye in the first round, which entitles these competitors to advance to the second round automatically without playing. Most of the time, these byes will be awarded to the highest-rated competitors in the event as a reward for some previous accomplishment; indeed, in some American team sports - most notably football - the number of teams qualifying forthea postseason tournament will be intentionally set at a number which is not a multiple of two, in order to provide such an advantage to a high-achieving team in the just-completed regular season.

Another key element in single-elimination tournaments is known as seeding. This is a technique that ensures that the highest-rated competitors will not be scheduled to play against one another until late in the tournament. In conjunction with seeding, brackets are set up, so that the top two seeds could not possibly meet until the final round (should either or both advance that far), none of the top four can meet prior to the semifinals, and so on.

Compare double-elimination tournament, round-robin tournament