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, since such tournaments are done for many non-sport games.
A round-robin tournament is a type of competition in which every competitor plays one match against every other competitor, either all others in the entire tournament or a specified section of it, usually called a group or pool.
Sometimes a tournament will start with a period of round-robin play, followed by two or three rounds of single-elimination play, with the highest finishers from the former advancing to the latter. This hybrid format is used in the World Cup of soccer, and in many events at the Olympic Games.
A hybrid round-robin, single-elimination tournament will almost always begin with an even number of contestants, but not necessarily a number which is a power of two like eight or 16; for example, twelve participants may begin play, divided into two groups or pools of six each. The round-robin portion of the tournament would then involve every player or team in a given group playing every other player or team within the same group once each. At the end of this segment, the top two in each group may advance to single-elimination - which would then consist of only a semifinal and final round - or the four highest finishers in each group may qualify for the single-elimination, which in that case would involve the use of a quarterfinal round as well.
One frequently-encountered problem in round-robin setups involves what to do if two (or more) contestants finish in a tie for the lowest position within the group that would qualify the player or team for the single-elimination phase. Then tie-breaking procedures come into play; if two are tied whichever of them won the head-to-head match they had played against each other might be given priority, which is simple enough; but in situations where more than two are tied the scenarios may become various and complicated (this situation is less likely to arise in sports where drawn or tied contests are permitted, in which case there would be a greater range of possible records a team could have once the round robin was completed).
Besides the potential for controversies that tie-breaking systems may create, the round-robin format is often criticized on other grounds; for example, some matches in the latter stages of a round robin may involve contestants who have already qualified for the elimination phase; if such a competitor is facing an opponent who is still trying to advance, the former may not give an all-out effort, thus affecting the outcome of the battle for the remaining spots. Even more ominously, a participant already assured of a spot in the next phase may deliberately lose, or tank, a match late in the round robin, in order to avoid facing a particular opponent in the eliminations, the pairings for which are often determined by the final standings of the round-robin groups.
In some competitions - most notably chess tournaments - only a round robin is contested, with no elimination phase to follow; in this case, the player with the best won-lost-drawn record at the end of the round robin is declared the winner.
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