Round robin

A round robin is a tournament format where each team plays against each other team once. In a round robin, 2n - 1 rounds are needed for 2n teams or 2n - 1 teams.

Round robins are the building blocks for many invitational tournament formats. An experienced tournament director will be familiar with the round robin structure, and can set up a round robin on the fly to handle a last-minute change in the number of teams.

Considerations

Round robin play ensures that teams in the same round robin pool play against the same opponents, so there is less concern with strength of schedule. This allows PPG to be used as a tiebreaker rather than PPB - head to head tiebreakers should be avoided if possible, as they double count the results of individual games, but this is not unique to round robins.

Though round robins ensure that all the teams in a pool have a comparable schedule, it does not make any assurances about the relative strength between pools. Using a format involving round robins does not eliminate the need for seeding.

The use of round robins in brackets is standard practice and is often implied to be the format used - hence, tournament formats can frequently be described in terms of just their bracket sizes. For example, consider a 16 team tournament which has two prelim brackets of 8 followed by rebracketing into four brackets of 4 for a total of 10 games + a final if needed. This can be referred to as simply 8x2 ("eight by two") into 4x4 ("four by four"), with the final being implied.

How to set up a round robin

In its simplest form, a round robin can be constructed for any even number of teams as follows. In this example, we will show a 10-team round robin.

First, number the teams from 1 to 10. As with any sensible 10-team format, this will require 5 rooms. Number them from 1 to 5.

Then, "snake" the teams in the schedule as follows:

Round 1

Room	Team 1	Team 2
Room 1	1	10
Room 2	2	9
Room 3	3	8
Room 4	4	7
Room 5	5	6

Each pairing represents a game played in the first round. To determine the next round's pairings, leave team 1 fixed and rotate the other teams clockwise, such that team 2 is where team 3 was the previous round, team 3 is where team 4 was, etc.

Repeating this procedure yields the following for rounds 2 through 4:

Round 2

Room	Team 1	Team 2
Room 1	1	9
Room 2	10	8
Room 3	2	7
Room 4	3	6
Room 5	4	5

Round 3

Room	Team 1	Team 2
Room 1	1	8
Room 2	9	7
Room 3	10	6
Room 4	2	5
Room 5	3	4

Round 4

Room	Team 1	Team 2
Room 1	1	7
Room 2	8	6
Room 3	9	5
Room 4	10	4
Room 5	2	3

This continues until the final round, where team 1 plays against team 2.

The result of of this procedure is the following 9 game schedule:

Round	Room 1	Room 2	Room 3	Room 4	Room 5
Round 1	1 v 10	2 v 9	3 v 8	4 v 7	5 v 6
Round 2	1 v 9	10 v 8	2 v 7	3 v 6	4 v 5
Round 3	1 v 8	9 v 7	10 v 6	2 v 5	3 v 4
Round 4	1 v 7	8 v 6	9 v 5	10 v 4	2 v 3
Round 5	1 v 6	7 v 5	8 v 4	9 v 3	10 v 2
Round 6	1 v 5	6 v 4	7 v 3	8 v 2	9 v 10
Round 7	1 v 4	5 v 3	6 v 2	7 v 10	8 v 9
Round 8	1 v 3	4 v 2	5 v 10	6 v 9	7 v 8
Round 9	1 v 2	3 v 10	4 v 9	5 v 8	6 v 7

For an odd number of teams, use the same procedure for one more than the number of teams, and choose one team (typically team 1) to treat as a bye. Teams playing the team 1 will then get a bye.

The simplest way to assign matches to rooms is to have the first column represent one room, the second column a second room, and so on. However, for a round robin with an even number of teams, this can be undesirable because team 1 is kept in the same room all day. There are pre-made round-robin schedules available to spread the teams evenly across rooms as much as possible (which is impossible for four teams).

Examples

Certain uses of the round robin are very common for specific numbers of teams.

Double round robin

In a double round robin, every team plays every other twice. This is common in college tournaments with six teams, as a tournament which is only able to draw that many teams is likely hard enough for 10 games to be a reasonable number (compare this to, say, an IS set, which is short and easy enough to reasonably allow 12+ rounds). 6-team tournaments which desire more games can have an advantaged final or break ties.

This format is not particularly amenable to an odd number of teams because it forces multiple byes, so tournaments in this situation may split a team or field a house team.

Triple round robin

In a triple round robin, every team plays every other thrice. This is usually only found in regions with only a small number of established teams, with the most common scenario being 4 teams playing 9 games.

The aforementioned flaws with double round robins are more extreme in triple round robins.

Full round robin

A full round robin eschews a prelim/playoff format in favor of one large round robin of every team. This simple format removes the need for seeding, guarantees that every team can play every other, and limits the number of byes per team to one, but limits the number of games played between the top teams; tournaments are rarely willing to make this tradeoff. It is much more common for teams to be sharply stratified, in which case additional rounds against comparable opponents is more valuable. The nature of a full round robin also means that there must either be a relative low number of teams or a strong willingness to play late into the night.

A combination of all these factors meant that, for many years, the Chicago Open preferred to use a full round robin followed by a final, if necessary. This was the format used almost every year between 2004 and 2015, at which point the tournament attracted enough teams that it was no longer feasible to avoid bracketing. 2012 CO, 2013 CO, and 2015 CO share the record for longest with 16 games and 17 teams each.

The only exception in this period was 2009 CO, which split its 14 team field into two prelim brackets and then rebracketed into an upper and lower bracket + advantaged final. 2006 CO had few enough teams (9) that a full round robin was able to be followed by round robins in the 4 team upper bracket and 5 team lower bracket, capped off by a two game advantaged final.

External links

• Balanced round robin schedule templates
• Scheduling Guide by Berkeley quiz bowl
• PACE FQBU Easy Round Robin Scheduling
• Round robin schedule generator