Editing Rules of Go (section)

==== Self-capture ====
'''Step 3 of a play. (After playing their stone and capturing any opposing stones) a player removes from the board any stones of their own color that have no liberties.'''

'''''Optional Rule 7A. A play is illegal if one or more stones would be removed in Step 3 of that play.'''''

The removal of one or more stones in Step 3 is called ''self-capture'', or ''suicide''. Most rulesets give effect to Optional Rule 7A, which prohibits it. This means that, in those rulesets, any play which under the basic rules would require a self-capture to be performed is illegal. For further information, see {{section link||Suicide}} below.

First an example which, it is emphasized, does ''not'' involve self-capture. When Black plays at ''a'', the capture of the marked white stones results in the black chain at the bottom right acquiring liberties. This move is legal (with the same result) whatever the rules.

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |   |   |  r
|  b|  b|  b|  b|  b
|  b| wT| wT| wT| wT
|  b| wT| dA|  b|  b|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |   |   |  r
|  b|  b|  b|  b|  b
|  b| wT| wT| wT| wT
|  b| wT| b1|  b|  b|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |   |   |  r
|  b|  b|  b|  b|  b
|  b|   |   |   |  r
|  b|  d| b1|  b|  b|24}}
|-valign="top"
|Before
|&nbsp;&nbsp;
|Black plays
|&nbsp;&nbsp;
|After capture
|}

The previous example shows that it is important that Step 2 of a play (capture) precedes Step 3 (self-capture). If the order were reversed, then self-capture would occur here.

If a play results in the capture of opposing stones, self-capture will not occur. A newly placed stone only removes a liberty from chains which it is adjacent to; thus, a chain can only be captured if it contained a stone adjacent to the newly placed stone. The removal of that adjacent opposing stone creates a liberty for the newly placed stone, which is now a part of the chain(s) of its own color that lost a liberty when it was placed. Thus, all of those chains, which are now one chain, still have at least one liberty. 

Now some examples of plays in which self-capture occurs. These moves would be illegal under the optional rule prohibiting suicide.

In this example, if Black plays at ''a'', then the stone played by them is removed immediately. This move has the same effect on the position as a pass, though it would not allow White to end the game by passing next (Rule 9). The move is in any event illegal by Rule 8. (This is the positional superko rule. This move might be legal under other versions of the superko rule. See {{section link||Repetition}} below.)

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |  b|   |  r
|  b|   |  b|   |  r
|  w|  w|   |   |  r
|dlA|  w|  d|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |  b|   |  r
|  b|   |  b|   |  r
|  w|  w|   |   |  r
| b1|  w|  d|  d| dr|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  u|  u| ur
|  l|   |  b|   |  r
|  b|   |  b|   |  r
|  w|  w|   |   |  r
|dlA|  w|  d|  d| dr|24}}
|-valign="top"
|Before
|&nbsp;&nbsp;
|Black plays
|&nbsp;&nbsp;
|After self-capture; violates Rule 8
|}

In the next example, Black plays at ''a'', resulting in the self-capture of the marked black stones.

{|border="0" cellspacing="0" cellpadding="0"
|-valign="top"
|
{{Go board 5x5
| ul|  u|  w|  u| ur
|  l|   |  b|   |  r
|  l|  b|  w|  w|  w
|  l|  w| bT|  A|  w
|  b|  d|  w| bT| bT|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  w|  u| ur
|  l|   |  b|   |  r
|  l|  b|  w|  w|  w
|  l|  w| bT| b1|  w
|  b|  d|  w| bT| bT|24}}
|&nbsp;&nbsp;
|
{{Go board 5x5
| ul|  u|  w|  u| ur
|  l|   |  b|   |  r
|  l|  b|  w|  w|  w
|  l|  w|   |  A|  w
|  b|  d|  w|  d| dr|24}}
|-valign="top"
|Before
|&nbsp;&nbsp;
|Black plays
|&nbsp;&nbsp;
|After self-capture
|}