Editing Go (game) (section)

=== Ko fighting ===
[[File:Gokof.png|thumb|A simplified ko fight on a 9×9 board. The ko is at the point marked with a square—Black has "taken the ko" first. The ko fight determines the life of the A and B groups—only one survives and the other is captured. White may play C as a ko threat, and Black properly answers at D. White can then take the ko by playing at the square-marked point (capturing the one black stone). E is a possible ko threat for Black.]]

In situations when the [[Ko rule]] applies, a ko fight may occur.{{sfn|Kim|Jeong|1997|pp=144–147}} If the player who is prohibited from capture is of the opinion that the capture is important because it prevents a large group of stones from being captured for instance, the player may play a ''ko threat''.{{sfn|Kim|Jeong|1997|pp=144–147}} 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. Their 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 they do not think it important or because there are no moves left that could function as a ko threat, they have ''lost'' the ko, and their 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.{{sfn|Kim|Jeong|1997|pp=144–147}} They thereby win 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.<ref name="Tavernier">{{cite journal
 | url = https://www.britgo.org/files/bgj/bgj110.pdf
 | title = Analyzing Ko Struggles Theoretically
 | first = Karel
 | last = Tavernier
 | date = Spring 1998
 | access-date = 8 October 2013
 | journal = British Go Journal
 | issue = 110
 | page = 11
 | archive-url = https://web.archive.org/web/20150131052153/https://www.britgo.org/files/bgj/bgj110.pdf
 | archive-date = 31 January 2015
 | url-status = live
}}</ref>

Frequently, the winner of the ko fight does not connect the ko but instead captures one of the chains that constituted their opponent's side of the ko.{{sfn|Kim|Jeong|1997|pp=144–147}} In some cases, this leads to another ko fight at a neighboring location.