Go Tactics - Ko Fighting

Ko Fighting

In situations where the ko rule applies, prohibiting a player to capture to avoid repetition, a ko fight may occur. If the player who is prohibited from capture is of the opinion that the capture is important, for example because it prevents a large group of stones from being captured, the player may play a ko threat. This is a move elsewhere on the board that threatens to make a large profit if the opponent does not respond. If the opponent does respond to the ko threat, the situation on the board has changed, and the prohibition on capturing the ko no longer applies. Thus the player who made the ko threat may now recapture the ko. His opponent is then in the same situation, and can either play a ko threat as well, or concede the ko by simply playing elsewhere. If a player concedes the ko, either because he does not think it important, or because there are no moves left that could function as a ko threat, he has lost the ko, and his opponent may connect the ko.

Instead of responding to a ko threat, a player may also choose to ignore the threat and connect the ko. He thereby wins the ko, but at a cost. The choice of when to respond to a threat and when to ignore it is a subtle one, which requires a player to consider many factors, including how much is gained by connecting, how much is lost by not responding, how many possible ko threats both players have remaining, what the optimal order of playing them is, and what the size — points lost or gained — of each of the remaining threats is.

Frequently, the winner of the ko fight does not connect the ko but instead captures one of the chains which constituted his opponent's side of the ko. In some cases, this leads to another ko fight at a neighboring location.