I had actually picked out this game before I saw John’s choices for last week, so I did not know he was going to be choosing a game with a rules dispute. The following is an extract from the GoGoD Encyclopaedia.
After Game 2 of the 25th Honinbo title match in 1970, the go historian and Kido editor, Hayashi Yutaka, started a dispute in the Mainichi Shinbun (evening issue of 9 June) about whether the final fill-in move 264 was actually necessary. Since playing it meant that Black won by 0.5 it was clearly important, though the two players appear to have had no part in the controversy. In the actual game, when Rin Kaiho played 263, Sakata looked hard at the position for a while, then said, "I need to fill in, don't I" and played 264 with no apparent doubt. What he had seen was that if he had neglected this move, Black (Rin) could have started a yose-ko by playing there himself. However, it is possible that Sakata did this only because he thought he had won anyway. When his half-point loss was revealed, he looked astounded.
Hayashi's argument was that the Nihon Ki-in rules specified that a true ko had to be filled in at the end of the game, even if one one player had a surplus of ko threats and could keep the ko open (so as to count the empty point as territory). This was the result of the eventual ruling in the Go-Iwamoto dispute of 1948 (and in the Go-Takagawa dispute of 1959): an open ko had to be filled in irrespective of the surplus or otherwise of ko threats. However, it seems that a fill-in move was not specifically required in the case of a yose-ko, and there was no reference in the rules to ko threats (of which Black had a surplus here, as it happened). Hayashi maintained that Sakata could have used this fact to claim that he didn't have to fill in the yose-ko, the game apparently being ended QED as soon as the yose-ko appeared on the board. This claim was countered, presumably on behalf of the Nihon Ki-in, by Kano Yoshinori, also in the Mainichi Shinbun. Preposterous as it would have been in practice, it did at least highlight the fact that the Nihon Ki-in had not kept their promise to Go Seigen to tighten up its rules on the matter.
Hayashi published his final thoughts in issues 9 and 10 of Kido in 1970 under the heading, "Tradition and logic in the Japanese rules of go - discussion of the endgame, dame and local life and death".

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No aji, keshi, kifu or kikashi has been harmed in the compiling of this post.
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