The first round is either drawn at random or seeded according to some prior order, such as rating (in chess) or last year's performance. All participants then proceed to the next round in which winners are pitted against winners, losers are pitted against losers, and so on. In subsequent rounds, each competitor faces an opponent with the same, or almost the same, cumulative score. No player is paired up with the same opponent twice. In chess the pairing rules try to ensure that each player plays an equal number of games with white and black, alternate colors in each round being the most preferable, and a particular effort is made not to assign a player the same color three times in a row.
During all but the first round, competitors are paired based on approximately how well (or poorly) they have performed so far. In the first round, competitors are paired either randomly or according to some pattern that has been found to serve a given game or sport well. If it is desired for top-ranked participants to meet in the last rounds, the pattern must start them in different brackets, just the same as is done in seeding of pre-ranked players for a single elimination tournament. In subsequent rounds, competitors are sorted according to their cumulative scores and are assigned opponents with the same or similar score up to that point. Some adjustments may be made to assure that no two players ever oppose each other twice, or to even out advantages a player may have due to chance.
The detailed pairing rules are different in different variations of Swiss system. They may be quite complicated, so to make the task easier, quicker and more accurate, the tournament organizer often uses a computer program to do the pairing.
In chess, a specific pairing rule, called "Dutch system" by FIDE, is often implied when the term "Swiss" is used. The Monrad system for pairing is commonly used in chess in Denmark and Norway, as well as in other sports worldwide. These two systems are outlined below.
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). Players are sorted by score groups, ranked and top half paired to bottom half. It is suggested that for smaller 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. 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.
There are a fixed number of rounds. After the last round, players are ranked by their score. If this is tied then a tie-break score, such as the sum of all their opponents' scores (Buchholz chess rating), can be used: see Tie-breaking in Swiss system tournaments.
Assuming no drawn games, determining a clear winner (and, incidentally, a clear loser) would require the same number of rounds as a knockout tournament, that is the binary logarithm of the number of players rounded up. Thus three rounds can handle eight players, four rounds can handle sixteen players and so on. If fewer than this minimum number of rounds are played, it can happen that two or more players finish the tournament with a perfect score, having won all their games but never faced each other.
Compared to a knockout tournament, a Swiss system has the advantage of not eliminating anyone: so a player who enters the tournament knows that he can play in all the rounds, regardless of how well he does. The only exception is that one player is left over when there is an odd number of players. The player left over receives a bye: he/she does not play that round but is usually awarded the same number of points as for winning a game (e.g. 1 point for a chess tournament). The player is reintroduced in the next round and will not receive another bye.
Another advantage compared to knockout tournaments is that the final ranking gives some indication of the relative strengths of all contestants, not just the winner of the tournament. As an example, the losing finalist in a knockout tournament may not be the second best contestant; that might have been any of the contestants defeated by the eventual tournament winner in earlier rounds.
In a Swiss system tournament, sometimes a player has such a great lead that by the last round he is assured of winning the tournament even if he loses the last game. This has some disadvantages. First, a Swiss-system tournament does not always end with the exciting climax of a knockout final. Second, this unmotivated first-place player may lose their final game, thus affecting the standings of other players. One fairly common fix for this issue is to hold single elimination rounds among the top scorers. In Scrabble tournaments a player with such a strong lead will often be paired against the highest-placed player who cannot possibly finish in the prize-winning zone; this process is known as Gibsonization (also known as the Gibson Rule) after it was first applied to the U.S. Scrabble Champion David Gibson in the 1995 All-Stars tournament. He is the all-time top money winner in the history of Scrabble, and earned a particular reputation by clinching victory in major events before the final round. Because of this, players are said to be Gibsonized: after winning, they are paired with lower-ranked players to avoid affecting the ranking of runners-up. A disadvantage compared to an all-play-all tournament is that, while the players finishing near the top are typically those with the best performances, and those finishing near the bottom are those with the worst performances, the players in the middle tend to be jumbled with little meaningful order. For example, at a recent European Chess Championship, players scoring 5½/11 had performance ratings ranging from to 2189 to 2559; such a difference suggests that the stronger-performing player would score more than 90% against the weaker-performing one. One player with a 2441 performance rating scored two and a half points better than one performing at 2518.
In Swiss system tournaments, the later rounds have a much greater bearing on the final results than the earlier rounds. In fact, it can even be an advantage to have a poor start to a Swiss system tournament because the player is then more likely to be paired against weaker opposition. Chess players colloquially refer to this as a "Swiss Gambit".
The system is used for selection to the English national pool team. Sixty-four players start the tournament and after six rounds, the top player will qualify as they will be unbeaten. The remaining seven places are decided after a series of round robins and play-offs.
Compared with a round-robin tournament, a Swiss can handle many players without requiring an impractical number of rounds. An elimination tournament is better suited to a situation in which only a limited number of games may be played at once, e.g. tennis. In a Swiss system, all players can be playing at the same time.
Due to the unpredictability of the pairings, the Swiss system is not suitable for events where fixtures need to be booked in advance, such as football tournaments.
The method of accelerated pairings also known as accelerated Swiss 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 and has the effect of reducing the number of players with perfect scores more rapidly (by approximately a factor of 2 after two rounds).
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.
Standard Swiss system
#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
After two rounds, the standings are:
#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
After two rounds, the standings are:
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 Swiss 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, a flexible system called a Konrad tournament can be used. A player's final score is based on his 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. This system is used by a few chess clubs in Norway.
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 has been used in Hardcourt Bike Polo. Currently Podium is the most frequently used for seeding a two-day tournament. The site allows you to track games and can be viewed from mobile devices at the tournaments or across the world.
The Swiss system is also used in some bridge tournament events, usually teams matches where a team consists of four players (two pairs) or more. In each round, one team plays against another team for several hands, with the North/South pair(s) of one team playing against the East/West pair(s) of the other team. The same hands are played at each table, and the results at the two (or more) tables are compared using the International Match Point (IMP) scoring system. The difference between the total IMPs scored by the two teams in that round is converted by a formula to victory points (VPs), with typically 20 VPs shared between the two teams, depending on the IMPs difference. 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. 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.
In chess, each player is pitted against another player who has done as well (or as poorly) as he or she has done. The first round is either drawn at random or seeded according to rating. Players who win receive a point, those who draw receive half a point and losers receive no points. Win, lose or draw, all players proceed to the next round where winners are pitted against winners, losers are pitted against losers and so on. In subsequent rounds, players face opponents with the same (or almost the same) score. No player is paired up against the same opponent twice, however. In chess, the rules 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 with number 5, number 2 is paired with number 6 and so on. Modifications are then made to balance colors and prevent players from meeting each other twice. 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.
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.
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-style 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.
On June 1, 2016 ESL announced that it would be using the Swiss system for its 2016 ESL One Cologne Counter-Strike: Global Offensive major tournament qualifiers. ELEAGUE also adopted this system for the 2017 ELEAGUE Major qualifier and the ELEAGUE Major itself.
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.
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 they are 4 or more players.
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.
Another Scrabble system based on Swiss pairing is known as "Chew pairing", and has been used at recent North American National and Canadian National Scrabble championships, and since 2005 at the World Scrabble Championship. Simulations are performed to determine which players are still in contention for each prize and those players are paired so as to balance the right of a low-ranked player to avoid elimination by challenging a high-ranked player with the right of high-ranked players to compete directly with each other for prizes.
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, three playoff rounds (in groups of 8) are played to determine the final placement of the teams.
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.