Diagonal Tournament Format.

The Diagonal Tournament Format was developed on this site based on the tournament experiences since 2011 and used for six years now (2021-2026).
Format description finished Oct. 2024.

Background.

If all the players are ordered by rating in a Round Robin table, then broadly speaking the outcomes of most games in the NE and SW parts of the table can be predicted beforehand, since the games are played by players with a large difference in rating.

Only the outcomes of games along the NW–SE diagonal are unknown, since the games are played by players of nearly equal strength.

So this format concentrates on those latter games and skips most of the rest.

Experience with the Diagonal Format.

The games are remarkably well played all across the board. Opponents of similar strength have an opportunity to show their very best and probably have more fun too, and no matter where they are on the rating scale the games are certainly interesting to watch.

The format handles any number of players, a large number as easily as a small number.

All players meeting their near neighbours on both sides effectively forms one long continuous chain of groups of 3–5 players all the way from top to bottom, with every player in the middle of his group.

Since all the players are activated with decisive games from start and all results are carried over to next rounds, the players have fewer opponents at a time and thus more time for the games.

Double Elimination.

Since two games must be played against each opponent, one black and one white, a defeat to two opponents corresponds to four lost games.

Performance Rating.

When the tournament has finished, the tournament result can be calculated for all the players by their Performance Ratings.

Tournament Setup.

Round 1.

All players are ordered in a row by their maximum ratings for this variant.

The Whisk setup:
All games are against equals, "Battle of Brothers".
In the first half of the row, each player plays against two nearby players.
In the second half of the row, each player plays against four nearby players.
The difference is because the opponents in the first half-row are roughly double as strong as the opponents in the second half-row.
The numbers of opponents are 2 2 2 ... 2 2 3 3 3 3 4 4 4 ... 4 4 4.

   00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23
00     x  x
01  x        x
02  x           x
03     x           x
04        x           x
05           x           x
06              x           x
07                 x           x
08                    x           x
09                       x           x
10                          x           x     x
11                             x           x     x
12                                x           x     x
13                                   x           x     x
14                                x     x           x     x
15                                   x     x           x     x
16                                      x     x           x     x
17                                         x     x           x     x
18                                            x     x           x     x
19                                               x     x           x     x
20                                                  x     x           x  x
21                                                     x     x        x  x
22                                                        x     x  x     x
23                                                           x  x  x  x

Round 2.

Players with four or more lost games are eliminated.

Again the Whisk setup but widened a step.
All games are against equals next in line, "Battle of Family".
The numbers of opponents are again 2 2 2 ... 2 2 3 3 3 3 4 4 4 ... 4 4 4.
If possible, players who have already met are not paired against each other again.

   00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16
00           x  x
01        x        x
02     x              x
03  x                    x
04  x                       x
05     x                       x
06        x                       x     x
07           x                       x     x
08              x                       x     x
09                 x                       x     x
10                    x                       x     x
11                       x                       x  x
12                    x     x                    x  x
13                       x     x              x     x
14                          x     x        x     x
15                             x     x  x     x
16                                x  x  x  x

Round 3.

Players with four or more lost games eliminated.

The Whisk setup, widened by another step.
All games are against equals further along the line, "Battle of Friends".
Numbers of opponents 2 2 2 ... 2 2 3 3 3 3 4 4 4 ... 4 4 4.
Again, if possible, players who have already met are not paired against each other again.

   00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22
00                 x  x
01              x        x
02           x              x
03        x                    x
04     x                          x
05  x                                x
06  x                                   x
07     x                                   x
08        x                                   x     x
09           x                                   x     x
10              x                                   x     x
11                 x                                   x     x
12                    x                                   x     x
13                       x                                   x     x
14                          x                                   x     x
15                             x                                   x  x
16                          x     x                                x  x
17                             x     x                          x     x
18                                x     x                    x     x
19                                   x     x              x     x
20                                      x     x        x     x
21                                         x     x  x     x
22                                            x  x  x  x

Round 4 ff.

Players with four or more lost games eliminated.
As more and more players are eliminated, still the same curve family is used and now gives set ups like

   00 01 02 03 04 05 06
00           x  x         
01        x        x
02     x              x 
03  x                 x
04  x              x
05     x        x
06        x  x

and

   00 01 02
00     x  x
01  x     x
02  x  x

New rounds continue using this method until a winner is found.

Losses are accumulated throughout the tournament.

The Winner.

Eventually only one player is left, the winner.

If all players are eliminated in the last round:
The player with the fewest losses won.
If two or more players have the same fewest number of losses:

Direct comparison of the games between the tied players, taking all rounds into account.
If this also results in a tie, the player who won the comparison with the shortest total game length across all rounds is the winner. (If a game was resigned, the number of moves it would take to finish the game is added.) If the game lengths differ by less than 10%, they're considered equal.
Or new rounds between the tied players until the winner is found.

Tournament Simulator.

The Diagonal Tournament Format can be tested with this tournament simulator:
Diagonal Tournament Simulator.

Aage Nielsen, October 26, 2022.
(Updated Aug. 18, 2026).