Round-robin tournament
[8] In sports with a large number of competitive matches per season, double round-robins are common.
There are also round-robin cricket, bridge, chess, draughts, go, ice hockey, curling, and Scrabble tournaments.
LIDOM (Baseball Winter League in the Dominican Republic) plays an 18-fold round robin as a semi final tournament between four classified teams.
Group tournaments rankings usually go by number of matches won and drawn, with any of a variety of tiebreaker criteria.
Frequently, pool stages within a wider tournament are conducted on a round-robin basis.
Examples with single round-robin scheduling include the FIFA World Cup, UEFA European Football Championship, and UEFA Cup (2004–2009) in football, Super Rugby (rugby union) in the Southern Hemisphere during its past iterations as Super 12 and Super 14 (but not in its later 15- and 18-team formats), the Cricket World Cup along with Indian Premier League, major Twenty-20 Cricket tournament, and many American football college conferences, such as the Conference USA (which currently has 9 members).
The group phases of the UEFA club competitions and Copa Libertadores are contested as a double round-robin, as are most basketball leagues outside the United States, including the regular season of the EuroLeague (as well as its former Top 16 phase); the United Football League has used a double round-robin for both its 2009 and 2010 seasons.
Season ending tennis tournaments also use a round robin format prior to the semi on stages.
The champion in a round-robin tournament is the contestant that wins the most games, except when draws are possible.
In theory, a round-robin tournament is the fairest way to determine the champion from among a known and fixed number of contestants.
The element of luck is seen to be reduced as compared to a knockout system since one or two bad performances need not ruin a competitor's chance of ultimate victory.
Final records of participants are more accurate, in the sense that they represent the results over a longer period against the same opposition.
This is helpful to determine the final rank of all competitors, from strongest to weakest, for purposes of qualification for another stage or competition as well as for prize money.
Moreover, in tournaments such as the FIFA or ICC World Cups, a first round stage consisting of a number of mini round robins between groups of 4 teams guards against the possibility of a team travelling possibly thousands of miles only to be eliminated after just one poor performance in a straight knockout system.
The top one, two, or occasionally three teams in these groups then proceed to a straight knockout stage for the remainder of the tournament.
In the circle of death it is possible that no champion emerges from a round-robin tournament, even if there is no draw, but most sports have tie-breaker systems which resolve this.
Round-robins can suffer from being too long compared to other tournament types, and with later scheduled games potentially not having any substantial meaning.
The main disadvantage of a round robin tournament is the time needed to complete it.
Other issues stem from the difference between the theoretical fairness of the round robin format and practice in a real event.
A notable instance of such an event was the 1950 FIFA World Cup match between Uruguay and Brazil.
Another disadvantage, especially in smaller round-robins, is the "circle of death", where teams cannot be separated on a head-to-head record.
[11] This famously happened during the 1994 FIFA World Cup Group E, where all four teams finished with a record of one win, one draw, and one loss.
games can be run concurrently, provided there exist sufficient resources (e.g. courts for a tennis tournament).
The circle method is a simple algorithm to create a schedule for a round-robin tournament.
[12] This schedule is applied in chess and draughts tournaments of rapid games, where players physically move round a table.
[13] The schedule can also be used for "asynchronous" round-robin tournaments where all games take place at different times (for example, because there is only one venue).
When the number of competitors is even, this schedule performs well with respect to quality and fairness measures such as the amount of rest between games.
On the other hand, when the number of competitors is odd, it does not perform so well and a different schedule is superior with respect to these measures.
[16] Berger published the pairing tables in his two Schach-Jahrbücher (Chess Annals),[17][18] with due reference to its inventor Richard Schurig.
Lucas, who describes the method as simple and ingenious, attributes the solution to Felix Walecki, a teacher at Lycée Condorcet.
