Match Handicap System
Historically in Japan, in longer multi-game matches, it used to be common for professional players of the same rank to alternate colors, rather than use komi, in order to offset the starting advantage. This system also allows for asymmetric assignment of colors (and handicaps), which was used to compensate strength differences.
Traditional System
Formulated by Honinbo Dosaku in the late 17th century.
| Rank difference | Name | Meaning |
|---|---|---|
| same rank | tagai-sen 互先 | Players alternate playing with black and white. |
| 1 rank (pro) | sen-ai-sen 先相先 | Weaker player takes black 2 out of every three games (BWB) |
| 2 ranks | josen 定先 | Weaker player takes black in all games |
| 3 ranks | sen-ni? 先二 | Weaker player always takes black, and takes 2 handicap every other game |
| 4 ranks | jo-ni? 定二 | Weaker player always takes 2 handicap |
| 5 ranks | ni-san? 二三 | Weaker player takes 2 and 3 handicaps alternately |
| 6 ranks | jo-san? 定三 | Weaker player always takes 3 handicap |
| 7 ranks | san-shi? 三四 | Weaker player takes 3 and 4 handicaps alternately |
| 8 ranks | jo-shi? 定四 | Weaker player always takes 4 handicap |
At first, the required margin to advance the handicap was "6 more wins or 4 straight wins". From the early 18th century, it became "4 more wins".
Oteai System
In 1924, Nihon Ki-in's rank promotion tournament, Joshiki Teai (Oteai from 1927) started and the following finer system of handicap was introduced:
| Rank difference | Name | Meaning |
|---|---|---|
| same rank | tagai-sen 互先 | Players alternate playing with black and white. |
| 1 rank (pro) | sen-ai-sen 先相先 | Weaker player takes black 2 out of every three games (BWB) |
| 2 ranks | josen 定先 | Weaker player takes black in all games |
| 3 ranks | sen-ni-sen 先二先 | Weaker player always takes black, and takes 2 handicap one out of every three games |
| 4 ranks | ni-sen-ni? 二先二 | Weaker player always takes black, and takes 2 handicap two out of every three games |
| 5 ranks | jo-ni? 定二 | Weaker player always takes 2 handicap |
| 6 ranks | ni-san-ni? 二三二 | Weaker player takes 2 handicap two out of every three games, and 3 handicap in the other game |
| 7 ranks | san-ni-san? 三二三 | Weaker player takes 3 handicap two out of every three games, and 2 handicap in the other game |
| 8 ranks | jo-san? 定三 | Weaker player takes 3 handicap in all games |
This system was invented by Murashima Yoshikatsu and has roughly one stone for every three ranks. Kansai Kiin used sen-sen-ai-sen (BBWB) instead of sen-ai-sen (BWB) for one rank difference. This is more logical as the midpoint between the two adjacent handicaps - two games at josen (BB) and two games at tagaisen (WB) combined.
In addition to the rank difference, it was common to change the handicap in a series of games if one player reached a sufficient lead, commonly 4 games, over the other. A player who was forced to take more handicap was said to have been "beaten down", and sometimes longer matches were canceled early to save face for a player who was at risk of being beaten down. A game in which a player was at such risk was known as a kadoban (cornered game) for that player.
In a mixed handicap, the more advantageous handicap game is called a tokuban (得番, game with advantage) and the less one is called a sonban (損番, game with disadvantage) or gyakuban (逆番, reversed game). For example, in ni-san-ni handicap, where 2 stone games and 3 stone games are mixed, 3 stone games are "tokuban" for the weaker player and "sonban" for the stronger.
In games from the GoGoD collection, the custom OH[] sgf tag is used to denote such handicaps, with parenthesis to indicate which match from the series is in the file. E.g. OH[B(W)B] means that the handicap is sen-ai-sen (BWB) and that this is the game in which the weaker player is playing with white.
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