Double-elimination tournament
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A double-elimination tournament is a competition in which a participant ceases to be eligible to win the tournament's championship upon having lost two games or matches. It stands in contrast to a single-elimination tournament, in which only one defeat results in elimination.
A double-elimination tournament is broken into two sets of brackets, the Winners Bracket and Losers Bracket (W and L Brackets for short; also sometimes Upper Bracket and Lower Bracket, respectively). After the first round, the winners proceed into the W Bracket and the losers proceed into the L Bracket. The W Bracket is conducted in the same manner as a single-elimination tournament, except of course that the losers of each round "drop down" into the L Bracket.
As with single-elimination tournaments, most often the number of competitors is equal to a power of 2 (4, 8, 16, etc) so that there are an even number of competitors at every round.
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[edit] Conducting the tournament
Each round of the L Bracket is conducted in two stages, the first stage consisting of the winners of the previous stage (or losers of the very first round of competition), the second stage consisting of the winners of the first stage against the losers of that same round of the W Bracket. This is to allow the losers of each stage of the W Bracket to "filter down" into the L Bracket.
For example, in an 8-competitor double-elimination tournament, the losers of the first round enter the first stage of the L Bracket --- the L Bracket quarterfinals --- and compete against each other. The losers are eliminated, while the winners proceed to the second stage of the L Bracket --- the L Bracket semifinals --- to face the losers of the W Bracket semifinals. The winners of the L Bracket semifinals proceed to the L Bracket finals, with the winner of that game being the Losers' Bracket champion.
The championship finals of a double elimination tournament is usually set up to be a possible two games. The rationale is that since the tournament is indeed double elimination, it is unfair to have the Winners' Bracket champion eliminated with its first loss. Therefore, while the Winners' Bracket champion needs to beat the Losers' Bracket champion only once to win the tournament, the Losers' Bracket champion must beat the Winners' Bracket champion twice.
In some tournaments, however, this game is winner-take-all, with the unfairness ignored.
The College World Series has frequently tried to modify this format to set up, if possible, a single championship game. Until the 1980s, the College World Series did this by adding an extra round to the Losers' Bracket. What would be the Losers' Bracket semifinals (i.e., the round where the Winners' Bracket semifinal losers dropped down) became the Losers' Bracket quarterfinals, with the Losers' Bracket semifinals having the two participants in the Winners' Bracket final (i.e., the WINNERS of the Winners' Bracket semifinals) drop down. This thus left open the possibility that the Winners' Bracket champion would pick up a loss, albeit in the Losers' Bracket semifinal. If, however, the Winners' Bracket champion prevailed in the Losers' Bracket semifinal, the same two-game final setup existed in effect, albeit not in practice ... for under the CWS pre-1980s version, the unbeaten Winners' Bracket champion would be playing a one-beaten Losers' Bracket opponent in the Losers' Bracket final, with the winner to advance to play the unbeaten Winners' Bracket champion in the finals (if necessary). The CWS subsequently broke up its eight-team filed into two four-team double elimination tournaments, with the winners meeting in either a sudden-death or, currently, a best-of-three final.
[edit] Pros and Cons
The double-elimination format has some advantages over the single-elimination format, most notably the fact that third and fourth places can be determined without the use of a consolation or "classification" match involving two contestants who have already been eliminated from winning the championship. A common criticism of the double-elimination format is that sometimes the last competitor to remain undefeated (i.e. the winner of the Winners Bracket) can actually lose only once and still be eliminated. However, that competitor does draw two byes during the course of the tournament, which many think compensates for that fact. This complaint is not an issue with full double elimination.
A disadvantage compared to the single-elimination format is that a considerably greater number of matches have to be conducted: since each player has to lose twice and since the tournament ends when only one player remains, in tournament for N competitiors there will be 2*N-1 (or 2*N-2 in case the winner was undefeated during the tourney) games; a plausible alternative is a single-elimination format where each match is a best-of-5 or best-of-7 series. This format still allows a competitor to lose (perhaps multiple times) while still remaining eligible to win the tournament. Of course, having multiple games in each series also requires considerably more games to be conducted.
Another (minor) disadvantage is that the double-elimination format is more difficult to understand and explain. However, once it is understood, then this becomes a moot point.
The most well-known athletic event that employs a double-elimination format is the NCAA baseball tournament, including the College World Series, where a team is not eliminated until it loses twice in each of the four rounds (regional, super regional 2-of-3 series, College World Series, and then championship 2-of-3 series). It is also extensively used in computer gaming tournaments (most famously by the Cyberathlete Professional League) and table football tournaments.
It is also used, in modified form, in the All-Ireland Senior Gaelic Football Championship and All-Ireland Senior Hurling Championship.
[edit] Variations
Some variations to double elimination are used. For example in Judo, where players that end up in the L bracket can finish third at best. The winner of the W bracket will win the tournament, with the losing finalist finishing second. The other losers of the W bracket will end up in the L bracket, which will only be played to the first stage of the final, resulting in two 3rd placed players. So compaired to the standard double elimination, there is no second stage of the final of the L bracked played, and there is no game between the winners of the W and L bracket.
Another aspect of the system used in Judo is, that losers of the first round (of the W bracket) only advance to the L bracket if the player they lost to, wins his or her second round match. If a player loses to a second round loser, they are eliminated from the tournament.
