Tournament
From Academic Kids

 For other uses, see Tournament (disambiguation).
A tournament is an organized competition in which many participants play each other in individual games. After each game, each participant is either dropped from the tournament, or advances to play a new opponent in the next "round." Usually, all the rounds of the tournament lead up to the "finals", in which the only remaining participants play, and the winner of the finals is the winner of the entire tournament.
A tournament is suitable for any competition in which two opponents (or two teams) face each other, such as football (soccer), tennis, basketball, debate, fencing, boxing, wrestling, contract bridge, board gaming, card gaming. Tournaments are popular for these competitions because they allow very large numbers of players to compete against each other, even though each particular game played is a competition between only two sides.
There are several popular tournament varieties. In the following examples, the term "player" is used, but the word "team" could have course be substituted if a team sport is being played. Likewise, some tournaments use a "game" for a single round, but some use a "match" which is best 2 games of 3, best 3 games of 5, or whatever is appropriate.
Some game clubs focus on preparing members for tournaments. Chess clubs, for instance, frequently employ similar ranking systems, chess clocks, and etiquette as those used in tournaments to prepare players for the atmosphere they will encounter.
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Singleelimination
Main article: Singleelimination tournament
Singleelimination tournaments are considered rather cutthroat. The loser of each game is dropped from the tournament. The winners move on to the next round. This continues until only two players are left, in which they play the round called the "finals", and the winner of this game is the winner of the entire tournament.
Doubleelimination
Main article: Doubleelimination tournament
Doubleelimination tournaments are less cutthroat than singleelimination tournaments, as a player is allowed to lose one game without being dropped from the tournament. The winners of the first round move on to play each other in the "winners' bracket" in the second round; the losers of the first round move on to the "losers' bracket" and play each other in the second round. In each subsequent round, those players in the "losers' bracket" who lose a game are dropped from the tournament, whereas those who win get to advance to the next round in the losers' bracket. Those players in the "winners' bracket" who win advance to the next round in the winners' bracket, and the losers drop down into the losers' bracket, to face opponents in that bracket. This continues until the finals, in which the winner of the winners' bracket, who is undefeated, faces the winner of the losers' bracket, who has lost one game so far. If the undefeated player loses this finals match, the match is repeated with the same two players to determine the winner once and for all, as a player is not dropped from a doubleelimination tournament unless he has lost twice. Sometimes, however, the second finalround match is not played, meaning that the player entering the finals undefeated can indeed lose only once and not win the tournament.
One notable event that uses a doubleelimination tournament is the College World Series, the NCAA baseball championship in the United States. In Division I, the highest level, the tournament proceeds in doubleelimination format until only two teams are left with fewer than two losses; the remaining teams then play a bestofthree series for the title.
Swiss style tournaments
Main article: Swiss system tournament
Swiss style tournaments seem more inclusive than single and doubleelimination tournaments, in that no player is ever forced to drop from the tournament. After each round, all players are matched up against other players with the same winloss record. So in the fifth round of play, all the 40 players compete against each other, all the 31 players compete against each other, etc., down to the players who are all 04, playing against each other. Generally the tournament continues until there is only one undefeated player, or sometimes for one or two rounds beyond that, in order to ensure that players who have previously lost a round (or two) could still win the tournament. (For fairness' sake, the number of rounds must be announced after the number of entrants is known but before the tournament begins.)
If the number of players is large, Swissstyle tournaments are easy for tournament organizers to run because there is less need to fill in slots of a bracket with "byes" (see below). A maximum of one bye is needed per round of a Swiss tournament, and that is only needed if there is an odd number of players competing in that round.
In some Swiss tournaments, the tournament continues for a certain number of rounds, at which point the main tournament ends and the top 8 players continue on to play an 8player single or doubleelimination playoff tournament for the victory.
At a certain point in a Swissstyle tournament, it becomes obvious to players when they have been mathematically eliminated from being able to win or place high, but they can continue playing if they choose  perhaps to boost their rating, if the tournament organizer reports player ratings to the sport's ratings authority.
A common variant of the Swissstyle tournament is known as the roundrobin tournament.
Brackets and initial matchups
Often a "bracket" is physically drawn on a sheet of paper or whiteboard for the benefit of spectators and players, especially in single and doubleelimination tournaments, showing who is playing whom, and making it easy to see who will be matched up in future rounds depending on who wins each game.
The easiest way for a tournament organizer to match up participants in the first round of a tournament is to do so randomly. However, a more satisfactory tournament (for spectators) can often be created by initially matching the best (or "top seeded") several players against players who are not in the "best" rank, and placing these players in the bracket such that it is probable that the best four players will end up playing each other in the semifinals.
Byes
By looking at a singleelimination bracket it quickly becomes clear that tournaments are easy to run only if they have a number of players which is a power of 2: i.e. 8, 16, 32, 64, 128, 256, etc. Having this exact number of players ensures that in each round, all players have somebody to compete against. In tournaments open to the general public, it is unlikely that this exact number of players will enroll, and in any case players may decide to voluntarily drop from the tournament at any point, so "byes" are used to fill holes in the bracket.
A player gets a bye when there is simply no opponent for him to play that round. Getting a bye is considered fortunate for a player; he is guaranteed to advance to the next round. Sometimes many byes are granted in a particular round because of holes in the bracket. The aim of the byes is to have the number of players be equal to a power of 2 in the next round, or possibly the round after that.
For example, in the bracket diagram shown above, suppose that Bert, Red, and Robert had never entered the tournament, resulting in a 13player tournament. One way of getting the number of players to a power of 2 as quickly as possible would be to match up all the players as shown in the first round, with Zaphod getting a firstround bye and advancing to the second round without having to play. In the second round, there are 7 players remaining; Monica receives a bye. Lisa, Ernie, Andrew, and Monica advance to the third round and now the number of players is a power of 2. The tournament can progress with no more byes.
In some tournaments, such as the playoffs of the NFL, byes are prizes to be earned by teams who do well in previous games that took place before the tournament. These teams get to skip the first round or two of the tournament, ensuring they can't be knocked out in an early upset.
Tiebreakers
Sometimes a "tiebreaker" statistic is needed to separate players who have the same winloss record, particularly for the purpose of awarding prizes to the top players. For example, after five rounds of play in a Swissstyle tournament, 4th through 7th places are often taken by players who all have a 32 record. Oftenused tiebreakers are score averages in the individual games played so far in the tournament, opponents' winning percentages, the total number of points scored by the player in the tournament, the total number of points scored by all the player's opponents in the tournament, and so forth. (The inability to boost one's tiebreaker statistics is considered the only disadvantage of receiving a bye in a previous round.)nl:Toernooi ja:トーナメント方式