Swiss-system tournament

The players are divided into groups, based on their score. Within each group with the same score, players are ranked, based on rating or some other criteria. Subject to the other pairing rules, the top half is then paired with the bottom half. For instance, if there are eight players in a score group, number 1 is paired with number 5, number 2 is paired with number 6 and so on. Modifications are then made to prevent competitors from meeting each other twice, and to balance colors (in chess).[5] Players are sorted by score groups, ranked and top half paired to bottom half. For this method to work, the score groups cannot be too small, and thus for smaller overall fields score groups are not a suitable approach.

The players are first ranked based on their score, then on their starting number (which can be random or based on seeding). Then #1 meets #2, #3 meets #4 etc., with modifications made to ensure that other rules are adhered to. Players are sorted by score (not score groups) and original rank, then each player paired to the next opponent, typically excluding repeats. This is more suitable for smaller numbers of competitors.

The Monrad system used in chess in Denmark is quite simple, with players initially ranked at random, and pairings modified only to avoid players meeting each other twice.[6] The Norwegian system has an optional seeding system for the first round pairings, and within a score group, the pairing algorithm endeavours to give players alternating colors.[7]

This pairing system is widely used in Scrabble and is known as the King Of The Hill format. It is considered to be distinct from the Swiss pairing system.

The method of accelerated pairings also known as accelerated Swiss[11] is used in some large tournaments with more than the optimal number of players for the number of rounds. This method pairs top players more quickly than the standard method in the opening rounds[11] and has the effect of reducing the number of players with perfect scores more rapidly (by approximately a factor of 2 after two rounds).[12]

For the first two rounds, players who started in the top half have one point added to their score for pairing purposes only. Then the first two rounds are paired normally, taking this added score into account. In effect, in the first round the top quarter plays the second quarter and the third quarter plays the fourth quarter. Most of the players in the first and third quarters should win the first round. Assuming this is approximately the case, in effect for the second round the top eighth plays the second eighth, the second quarter plays the third quarter and the seventh eighth plays the bottom eighth. That is, in the second round, winners in the top half play each other, losers in the bottom half play each other, and losers in the top half play winners in the bottom half (for the most part). After two rounds, about ⅛ of the players will have a perfect score, instead of ¼. After the second round, the standard pairing method is used (without the added point for the players who started in the top half).

As a comparison between the standard Swiss system and the accelerated pairings, consider a tournament with eight players, ranked #1 through #8. Assume that the higher-ranked player always wins.

#1 plays #5, #1 wins
#2 plays #6, #2 wins
#3 plays #7, #3 wins
#4 plays #8, #4 wins

#1 plays #3, #1 wins
#2 plays #4, #2 wins
#5 plays #7, #5 wins
#6 plays #8, #6 wins

#1 plays #3, #1 wins
#2 plays #4, #2 wins
#5 plays #7, #5 wins
#6 plays #8, #6 wins

#1 plays #2, #1 wins
#3 plays #5, #3 wins
#4 plays #6, #4 wins
#7 plays #8, #7 wins

Accelerated pairings do not guarantee that fewer players will have a perfect score. In round 2, if #5 and #6 score upset wins against #3 and #4, and there is a decisive result between #1 and #2, there will be three players with a perfect 2–0 score.

The Danish system works in principle like a Monrad system, only without the restriction that no players can meet for a second time, so it is always #1 vs. #2, #3 vs. #4 etc.

Bridge team tournaments, if not played as "Round Robin", usually start with the Swiss system to make sure that the same teams would not play against each other frequently, but in the last one or two rounds there is a switch to the Danish system, especially to allow the first two ranked teams to battle against each other for the victory, even if they have met before during the tournament.

In a few tournaments which run over a long period of time, such as a tournament with one round every week for three months, the Grand Prix system can be used. A player's final score is based on their best results (e.g. best ten results out of the twelve rounds). Players are not required to play in every round, they may enter or drop out of the tournament at any time. Indeed, they may decide to play only one game if they wish to, although if a player wants to get a prize they need to play more rounds to accumulate points. The tournament therefore includes players who want to go for a prize and play several rounds as well as players who only want to play an off game.[13]

A variant known as the McMahon system tournament is the established way in which European Go tournaments are run. This differs mainly in that players have a skill ranking prior to the start of the tournament which determines their initial pairing in contrast to the basic Swiss-system approach where all players start at the same skill ranking. The McMahon system reduces the probability of a very strong team meeting a very weak team in the initial rounds. It is named for Lee E. McMahon (1931–1989) of Bell Labs.

A tournament system in Italy. It is similar to the Swiss System, but doesn't split players based on their score. Before pairing any round, players are listed for decreasing score / decreasing rating, and the opponent of the first player in the list is the player following him by a number of positions equal to the number of remaining rounds, and so on for the other players. As consequence of this, the difference in rating between opponents at the first round is not so big (as for the accelerated systems), and ideally the "big match" between the first and the second one should occur at the last round, no matter how many players and rounds are in the tournament.

International Student Badminton Tournaments depend on the Swiss ladder system to ensure its players get as many challenging matches as possible over the course of the badminton tournament. The tournaments are meant to promote both the sport and the social aspect of the game, hence its results are not connected to external rankings. Beforehand, players can enroll in three or four categories designed to separate national, regional and recreational players. Players of different clubs are coupled to form doubles and mixed doubles. The starting positions on each ladder (singles, doubles and mixed doubles) are random. Unlike in official matches a 1–1 draw is possible and games are usually not extended after 21 is reached in order to maximise the number of played matches.

The Swiss system is used in some bridge tournament events, usually team matches. In each round, one team plays against another for several hands with the North/South pairs playing against their opponent's East/West pairs. The same hands are played at each table and the results compared using the International Match Point (IMP) scoring system. The difference between the total IMPs scored in the round is converted to Victory Points (VPs), with typically 20 VPs shared between the teams.

In the first round, teams are usually paired randomly; however, pairings can be based on other criteria. In subsequent rounds, the teams are ranked in order of the number of VPs they have accumulated in previous rounds, and the top team plays the second team, the third team plays the fourth team, etc., subject to the proviso that teams do not play each other twice.

Software may be employed to do pairings, and in the early rounds it will match teams with approximately the same score but it will not result in a precise 1 vs 2, 3 vs 4, etc. This is done so that matches can begin before all teams have finished the previous round. In later rounds, the pairings are slower but more exact. In the last one or two rounds there may be a switch to the Danish system to make sure that each team plays the final match according to its actual ranking, even if this results in some teams playing against an opponent a second time. At least in the US, this is extremely rare, usually employed only in small club games with a large number of rounds relative to the number of teams.

In chess, each player is pitted (paired) against another player with an equivalent performance score. In "Round 1" of a chess tournament paired using the Swiss System, players usually are seeded according to their known playing strength, for example their "chess rating" assigned to them by their local club, their national federation, or the world chess federation (FIDE). In some events, especially when none or few of the players have an official chess rating, the players are paired randomly. Once play begins, players who win receive a point, those who draw receive one-half of a point, and those who lose receive no points. Win, lose or draw, all players proceed to the next round where winners are pitted against opponents with equal performance scores (e.g. Round 1's winners play each other, Round 1's draws play each other, etc.). In later rounds (typical tournaments have anywhere from 3-9 rounds), players face opponents with the same (or almost the same) score. No player is paired up against the same opponent twice (unless the tournament is specifically designed for all players to play one another twice (once as White, once as Black).

The rules for Swiss System chess events also try to ensure that each player plays an equal number of games with white and black. Alternating colors in each round is the most preferable and the same color is never repeated three times in a row.

Players with the same score are ideally ranked according to rating. Then the top half is paired with the bottom half. For instance, if there are eight players in a score group, number 1 is paired to play number 5, number 2 is paired to play number 6 and so on. When the tournament, or a section of the tournament, has an odd-number of players, one player usually is assigned a "Bye"—e.g. a round where the player is not paired.  Modifications are then made to balance colors and prevent players from meeting each other twice.[1]

The first national event in the United States to use the Swiss system was in Corpus Christi, Texas in 1945; and the first Chess Olympiad using it was held in Haifa in 1976.[14]

In chess, the terms Swiss and Monrad are both used, and denote systems with different pairing algorithms. The Monrad pairing system is commonly used in Denmark and Norway, while most of the rest of the world uses one of the Swiss systems defined by FIDE. In most other sports, only one format is used, and is known either as Monrad or Swiss.

Croquet tournaments are frequently run using a Swiss system, often flexibly so that the order of players is not strictly maintained, avoiding players waiting around for long games to finish. Variants include the Burridge Swiss, used as a qualifying stage for a subsequent elimination, in which there is a predetermined threshold of games. Once a player reaches that threshold, the player will no longer be included in the Swiss and will have qualified. Once a player can no longer reach the threshold, they are eliminated from the Swiss. The number of rounds is about double that of the threshold.[15]

Curling uses a variation called the Schenkel system.

Like a Swiss tournament, the Schenkel ensures that after the first round teams will play against teams with similar levels of success so far. That means that after the first round the pairs for the second round would be first-ranked team against the second, third against fourth, and so on.

In a true Swiss tournament all teams play in one group. However, in a curling arena there are a limited number of curling sheets available at any one time. Therefore, the teams are usually divided into groups, and the groups are rearranged after a round or two.

The criteria used for ranking are, in order:

• points won (2 points for victory in a game, 1 point for a tie, none for a loss)
• total ends won so far
• total stone-points scored
• stone ratio (stone-points scored minus stone-points conceded)

British Parliamentary Style debate competitions have four rather than two teams in each debate. The preliminary round for many such competitions, including the World Universities Debating Championship, ranks teams by a modified form of Swiss tournament, usually called a tab. "Tab" also denotes to the software used for scheduling of rounds and tabulation of results. Teams are ranked from first to fourth in each debate and awarded from three down to zero points. Teams with similar points totals are grouped off for each successive round. Just as chess Swiss tournaments are arranged to ensure players have a balance of playing with black pieces and white pieces, so too debate tournaments attempt to provide teams with a balance of places in the speaking order (i.e. Opening Government, Opening Opposition, Closing Government, and Closing Opposition). With four competitors rather than two, significantly greater compromise is required to balance the ideal requirements of, on the one hand, a team not meeting the same opponent twice and, on the other hand, a team having a balanced mix of places in the running order.

Mind Sports South Africa, the national body for esports in South Africa, uses a Swiss system for all its tournaments. For its Swiss implementations, players receive three points for a win and only one for a draw and no player can play against another player more than once. There is the further provision that no player may play against another player from the same club in the first round as long as no one club has 40% of the entrants. Overwatch Open Division also makes use of the Swiss system,[16] as well as the Hearthstone Global Games tournament.[17]

A variation of Swiss system common in esports tournaments sees participants play until reaching the preset number of wins or losses, instead of having everyone play the same amount of games. In this system, player or team that wins the required amount of games advances to the next stage of the tournament and doesn't play any more games in this stage; conversely, those who lose enough games are eliminated from the tournament. This system was used for the first time by ESL during qualifying rounds for the ESL One Cologne 2016 tournament,[18] and has been used since then in all Counter-Strike: Global Offensive Major Championships.[19] The format was also used for the Dota 2 Kiev Major tournament in 2017,[20] Magic: The Gathering Arena Mythic Championship tournaments,[21] and Gears of War Gears Esports Events.[22] This format is also used in the recent format of Rocket League's RLCS X's Fall Split.

Relatively few Go tournaments use the Swiss system. Most amateur Go tournaments, at least in Europe and America, now use the McMahon system instead. Swiss-system tournaments must start with very unequal matches in the early rounds—"slaughter pairing" is the name of one initial pattern used—if the Swiss pairing rules applied subsequently are to allow the top players to meet in the latest rounds. The McMahon system is designed to give all players games against similarly skilled players all along, and to produce final standings that more accurately reflect the true current skill levels of players.[2][23]

One of the two qualifying tournaments for the Gwent Open and Gwent World Masters, the official tournaments for the card game Gwent, partially employ the Swiss system. The Qualifier #2 consist of two days, the first of which is played with Swiss-system selection with best-of-three competition for each pair of players. The second round instead employs double elimination and best-of-five. The more exclusive Qualifier #1 only uses the double-elimintation, best-of-five format. The actual tournaments (Gwent Open and Gwent World Masters) are single-elimination best-of-five. Thus the Swiss system is only used as preselection for preselection (who gets to progress to day 2, who then gets to go to the tournament).[24]

The DCI, the tournament sanctioning body for the card game Magic: The Gathering, uses a Swiss system for most tournaments. Unlike with other Swiss implementations, players receive three points for a win and only one for a draw. After sufficient rounds to mathematically ensure that players with a record of one loss or better will be ranked in the top eight players, typically the top eight players advance to a single-elimination stage, with several statistics used as tie-breakers. The minimum number of players to top 8 are 16 or more, and top 4 with 8 players or more, and top 2 (if necessary) if there are 4 or more players.[25]

Grand Prix main events are split into two days. On day 1, eight or more Swiss rounds are played, where anyone with at least 18 match points (a record of 6-2 or better) will advance to day two. On day two, seven more Swiss rounds are played, followed by a cut to the top eight single elimination stage.

Tournaments in the Pokémon Trading Card Game and Video Game Championships use a combination of the Swiss system and single-elimination. The tournament begins as a Swiss-system tournament. At the end of the Swiss rounds, the top players advance to a single-elimination tournament (also known as the Top Cut). In previous years, the Top Cut would include between 12.5 and 25 percent of the original number of participants (e.g. if there were 64 to 127 players, there would be a Top 16).

As of the 2013–2014 season, Swiss rounds in City, State, Regional, National, and World Championships are played best-of-three, with a 50-minute plus three-turn time limit. Ties were introduced into the Swiss round portion of the tournaments in the 2013–2014 season for the first time since 2002–2003. A win is worth 3 match points, a tie is worth 1 match point, and a loss is worth 0 match points.

Top Cut rounds are played best-of-three, with a 75-minute plus three-turn time limit.

Also, the Regional and National Championships were contested as two-day Swiss tournaments, where only the top 32 players from Day One would continue in another Swiss tournament in Day Two, prior to a Top 8.

League Challenge and Pre-Release tournaments are played solely as a Swiss system. Local tournaments may or may not have a Top Cut.

The tiebreakers are in the order of Opponents' Win Percentage, Opponents' Opponents' Win Percentage, Head to Head, and Standing of Last Opponent. The fourth tiebreaker will always result in the tie being broken.

In some Scrabble tournaments, a system known variously as "modified Swiss", "Portland Swiss", "Fontes Swiss" or "speed pairing" is used, whereby first players are placed in groups of four, and play three rounds of round-robin play, and subsequently are paired as in Swiss pairing, but using the standings as of the second to last round, rather than the last round. This has the advantage of allowing the tournament directors to already know who plays whom by the time given players are finished with a round, rather than making the players wait until all players have finished playing a given round before being able to start the time-consuming pairing process.

Commonly used in Australia, and now in many other countries, is a system known as "Australian Draw". Whereby each round is paired using a normal #1 plays #2, #3 plays #4, etc. except that repeat pairings within a selected range of previous games is forbidden. Often, for shorter tournaments the selected range will be since the very first round of the tournament, thus never having a repeat pairing for the entire tournament. For longer tournaments it is also common to have the first N rounds use the Australian Draw system, and followed by one or more "King Of the Hill" rounds. "King Of the Hill" is a strict #1 plays #2, #3 plays #4, etc. with no regard to previous pairings, thus unlimited repeat pairings are allowed.

Although labelled as 'Australian Version of Swiss Pairing' it is more akin to the King Of The Hill pairing system, than to the Swiss - Dutch system. As in chess, when the term Swiss Pairing is used, it's usually a reference to the Swiss Dutch System.

In professional sumo in Japan, the six bi-monthly tournaments (本場所, honbasho) use a proprietary system similar to the McMahon system, with rikishi generally fighting those near their ranking on the banzuke; the winner of a division is the rikishi with the best record at the conclusion of tournament's 15 days. However, unlike other tournament utilizing a Swiss or McMahon system, match-ups are not determined by a formula but rather the desires of a committee of elders, with restrictions against repeat match-ups, bouts between close relatives like siblings, or bouts between members of the same stable.[26][27]

Windmill Windup, a three-day yearly Ultimate Frisbee tournament held in Amsterdam, was the first event in ultimate to introduce the Swiss draw system into the sport in 2005. In later years, many other tournaments started using this format, like Belgium's G-spot, Wisconsin Swiss and many others. For each round, teams earn victory points based on the score difference of their win (or loss). In this way, also a team clearly losing a game is encouraged to fight for every point in order to get more victory points. After each round, teams are ranked according to their victory points. Ties are broken by considering the sum of the current victory points of their opponents. In the next round, neighboring teams in the ranking play each other. In case they have played each other in a previous round, adjustments to the rankings are made. After five rounds of Swiss draw, the top 8 teams play three playoff rounds to determine the final placement of the teams. All other teams continue with the Swiss draw in the remaining rounds.

The International Wargames Federation, the international body for wargames, uses a Swiss system for all its tournaments. For its Swiss implementations, players receive three points for a win and only one for a draw and no player can play against another player more than once. There is the further proviso that no player may play against another player from the same country in the first round as long as no one country has 40% of the entrants. For national championships such rule is amended to read that no player can play against a player from the same club in the first round as long as no one club has 40% of the entrants.

Konami Digital Entertainment of the United States uses proprietary software for their sanctioned and official tournaments. Konami Tournament Software (KTS) is what is supplied to the Tournament Organizers to run each tournament. The software utilized the Swiss system similarly to Magic: The Gathering—3 points for a win, 1 for a draw, 0 for a loss.

Konami's official tournament policy dictates how many rounds are played based on the number of participants. After the set number of rounds of Swiss are complete, there is generally a cut to advance in the tournament. This is then played as single-elimination until a winner is declared.