Knock-out Tournaments
A knockout tournament is divided into successive rounds; each competitor plays in at most one fixture per round. The top-ranked competitors in each fixture progress to the next round. As rounds progress, the number of competitors and fixtures decreases. The final round, usually known as the final or cup final, consists of just one fixture; the winner of which is the overall champion.
In a single-elimination tournament, only the top-ranked competitors in a fixture progress; in 2-competitor games, only the winner progresses. All other competitors are eliminated. This ensures a winner is decided with the minimum number of fixtures. However, most competitors will be eliminated after relatively few matches; a single bad or unlucky performance can nullify many preceding excellent ones. Some single-elimination tournaments such as NBA use a multiple-game format, in which teams would play each other more than one game (e.g. best-of-seven series in NBA) in order to determine who is the winner of this round. Other knockout formats provide a "second chance" for some or all losers.
A double-elimination tournament may be used in 2-competitor games to allow each competitor a single loss without being eliminated from the tournament. All losers from the main bracket enter a losers' bracket, the winner of which plays off against the main bracket's winner.
Some formats allow losers to play extra rounds before re-entering the main competition in a later round. Rowing regattas often have repechage rounds for the "fastest losers" from the heats. The winners of these progress, but are at a disadvantage in later rounds owing to the extra effort expended during the repechage.
A family of tournament systems that grew from a system devised for the Victorian Football League, the historic predecessor to the Australian Football League (AFL), allow the teams with the best record before the playoffs to lose a game without being eliminated, whereas lesser qualifiers are not. Several of the most prominent leagues in Australia use such a system, such as the AFL, the National Rugby League in rugby league, and the A-League of association football. Similar systems are used in the Super League of European rugby league, cricket's Indian Premier League, and most curling tournaments.
In athletics meetings, fastest losers may progress in a running event held over several rounds; e.g. the qualifiers for a later round might be the first 4 from each of 6 heats, plus the 8 fastest losers from among the remaining runners.
An extreme form of the knockout tournament is the stepladder format where the strongest team (or individual, depending on the sport) is assured of a berth at the final round while the next strongest teams are given byes according to their strength/seeds; for example, in a four team tournament, the fourth and third seed figure in the first round, then the winner goes to the semifinals against the second seed, while the survivor faces the first seed at the final. Four American sports organizations either currently use this format, or have in the past:
- For over 30 years (generally from the mid-1960s to 1997), most events on the PBA Tour of ten-pin bowling used a stepladder final, usually involving five bowlers.
- Two U.S. college conferences operate a tournament format in basketball that combines two stepladder tournaments into one—that is, both halves of the bracket are organized as stepladder tournaments. The bottom four teams play in the first round; the survivors will face the #3 and #4 seeds, and the winners of those matches take on the top two seeds in the semifinals. This format was adopted by the West Coast Conference for its men's and women's tournaments in 2003, and by the Ohio Valley Conference for both sexes in 2011. Once the WCC expanded to nine teams with the entry of BYU in the 2011–12 academic year, the conference added one round to one half of the bracket for both tournaments starting in 2012.
- The now-defunct Women's Professional Soccer used this format in all of its three seasons of existence. For an example of its playoff system, see 2009 Women's Professional Soccer Playoffs.
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