The Illegal Move in Go

There is one kind of illegal move in Go, illustrated by the red spot at left. You may not put a stone in any place where there are no lines touching it or the other stones in its group. (A group is stones of all one color that touch; you can see some examples.)

You are not allowed to put a black stone in the red spot, because it would be completely surrounded. A black stone there would have to leave the Go board immediately. It could not remain on the board.

If you need proof, see the example of how to capture a stone in this same position.

You are allowed to put a white stone in the red spot, because all the other stones are white (so it would be part of a group) and there are lines touching the other white stones.

As with most rules, there is an important exception.

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