Swiss-system tournament

A Swiss-system tournament is a tournament which uses a non-elimination format. There are several rounds of competition, but considerably fewer rounds than in a round-robin tournament, so each competitor (team or individual) does not play every other competitor. Competitors meet one-to-one in each round and are paired using a predetermined set of rules designed to ensure that as far as possible a competitor plays competitors with the same current score, subject to not playing the same opponent more than once. The winner is the competitor with the highest aggregate points earned in all rounds.

A Swiss system may be used when it is not feasible to play as many rounds as required in a round-robin, but it is not desired to eliminate any competitors before the end of the tournament.^[1] This is the case for many tournaments of amateurs where the tournament's purpose is to provide playing experiences, and if continuing full use of facilities is not too expensive. On the other hand, if facilities are constrained or costly, if players are professionals who must be paid for their games played, and if the tournament's purpose is to present exciting matches of top contenders to a viewing audience, then single elimination would serve better. In a Swiss system there are a predetermined number of rounds and a predetermined scoring system. All competitors play in each round unless there is an odd number of competitors.

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 first tournament of this type was a chess tournament in Zurich in 1895, hence the name "Swiss system".^[1]

Swiss systems are commonly used in chess,^[1][2] bridge, eSports, Morabaraba, Scrabble, Backgammon, squash, Pétanque (boules), Quiz bowl, Magic: The Gathering,^[3] Policy Debate, Warhammer, eight-ball, Reversi, Dominion, Pokémon TCG,^[4] Yu-Gi-Oh,^[5] Blood Bowl, Guild Wars 2, Path of Exile, Android: Netrunner,^[6] and other games.

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][7]

Round-robin pairings are suitable for a small number of competitors and rounds, as most or all players will play each other. The underlying assumption is that the player who has played all possible opponents and ends with the highest score, must be the winner. Elimination, or sudden death, pairings rapidly reduces the number of competitors, but may not necessarily result in the best possible competitor winning. Simple survival may result in winning a competition against better opponents. Swiss systems intend to provide a clear winner with a limited number of rounds and a potentially unlimited number of opponents. A Swiss system draw should result in a clear winner, without having to play all opponents as in round robin, and without a single bad result terminating participation.

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.

Pairing procedure

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.^[8]

The detailed pairing rules are different in different Swiss systems. They may be quite complicated, so to make the task easier, quicker and less error prone, 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.

Dutch system

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 prevents competitors from meeting each other twice, and to balance colors (in chess).^[8] 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.

Monrad System

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.^[9] 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.^[10]

Final scores and tie-breaking

There are a predetermined 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.

Analysis, advantages, and disadvantages

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.^[11]

The system has been used for pool trialing in England. To overcome there being multiple players with the same perfect score, players are eliminated after a certain amount of losses. This causes a final match where only one player will end with a perfect score and automatically qualify, while the rest of the field will play a round robin to determine the final number of entrants.

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.

The primary disadvantage of a Swiss system is its complexity. For example it would not usually be suitable for a football tournament because for practical reasons, the fixtures need to be arranged in advance, with plenty of notice being given of each match.

Variations of Swiss systems

Accelerated pairings

The method of accelerated pairings also known as accelerated Swiss^[12] 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^[12] and has the effect of reducing the number of players with perfect scores more rapidly (by approximately a factor of 2 after two rounds).^[13]

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

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

Round 2:
#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: 2-0
2: 2-0
3: 1-1
4: 1-1
5: 1-1
6: 1-1
7: 0-2
8: 0-2

Accelerated pairings

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

Round 2:
#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:
1: 2-0
2: 1-1
3: 1-1
4: 1-1
5: 1-1
6: 1-1
7: 1-1
8: 0-2

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.

Danish system

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's 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.

Konrad system

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.^[14]

McMahon system

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 starts at different levels; so a Swiss system is the special case where all players start at the same level. It is named for Lee E. McMahon (1931–1989) of Bell Labs.

Amalfi system

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.

Application of the Swiss system

Badminton

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 mix doubles. The starting positions on each ladder (singles, doubles and mix 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.

Hardcourt bike polo

The Swiss-system has been used in Hardcourt Bike Polo. Currently Podium is the most frequently used for seeding a two-day tournament.^[15] The site allows you to track games and can be viewed from mobile devices at the tournaments or across the world.

Bridge

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 predetermined 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 paired essentially randomly. 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.

Chess

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.^[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.^[16]

Curling

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)

See: http://www.curlingcalendar.com/wiki/61

Debate tabs

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.

eSports

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 proviso 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.

Magic: the Gathering

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.^[17]

Pokémon

Tournaments in the Pokémon Trading Card Game 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.

Scrabble

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.^[18]

Ultimate Frisbee

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.

Wargames

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.

See also

• Tie-breaking in Swiss system tournaments

Other tournament systems

• Round-robin tournament
• Single-elimination tournament
• Double-elimination tournament
• Scheveningen system

References

External links

• Detailed rules from FIDE on the Swiss pairing system
• Comparison of Swiss and Round Robin formats