Oshirogo

Oshirogo (御城碁 "castle Go") or castle games were official matches of high-level Go played in Japan during the Edo period, usually in the castles of the shōgun. Players were mostly from the four go houses.

Matches were played in the shōgun's presence. With the passage of the years, this became a formality: the players would replay a game that had already been played, and the shōgun would often be represented by an official, rather than attend himself. The games themselves were, though, bitterly contested, since the castle games had a major effect on the prestige of the four houses. Throughout the Tokugawa shogunate there was an ongoing struggle to take control of the official positions of Meijin and godokoro.