This is a Japanese term from the game of Go (Wei Qi/Badouk). It refers to a sudden, often large, exchange of one person's potential territory for the other's. In other words, Black will get control of an area that used to be White's, but White will snatch a comparible amount of turf from Black.

Furikawari occurs most oftenly in one of two situations: either when someone builds a large moyo, or during a ko fight.

For the first situation, we must understand what a moyo is. A moyo is a framework of stones, loosely enclosing what might be thought of as "potential territory." It is not secure, by any means, but it is likely that at least some of it will turn into solid territory before the game is through. For more details, see my moyo writeup.

How a moyo can lead to furikawari is when the opponent decides to jump right in and attempt to invade it, rather than simply reducing it from the outside. The player with the moyo will then attack viciously, but if the invasion was properly read out, the invader should be able to live, destroying most of the moyo. The trade-off, however, is that the player whose moyo was destroyed will build lots of outside thickness while sealing off the invading group's escape routes. After the invasion lives, he might then use the strength he built up in this manner to stage an attack or invasion of his own, taking over a large amount of the opponent's territory to compensate for what he lost.

For the second, we must explain what a ko fight is. This is a bit more complicated, so it is probably best to check the ko and ko threat nodes to understand, but in a nutshell: in Go, situations can arise which would ordinarily lead to repetitive capture and recapture, allowing the game to go on forever unless one player breaks the pattern. To avoid this, the rules state that a board position can never be repeated. Therefore, if someone captures you in a "ko" situation, you must play elsewhere on the board before recapturing yourself. The general idea is to play a move so threatening that the opponent must answer it, so that you can then recapture the ko and so on, until someone runs out of ko threats or decides to ignore one of the opponent's.

A ko furikawari occurs when the value of a ko is so large that one player decides to ignore a huge (but hopefully slightly smaller than the ko) ko threat in order to win the ko. The opponent then follows through on his threat, destroying something of the first player's to compensate for the ko.

Here's an interesting example from one of my games. The nature of a furikawari is such that I need to show the whole goban. I was playing Black (x).

   a b c d e f g h j k l m n o p q r s t 
19 . . . . o x x . . . . . . . . . . . . 19
18 o o . o . o x . . x . x . . x x o . . 18
17 x o . o . o x . . . x o . x . . o . . 17
16 x o o . . x x . x x o o . x o o . o . 16
15 x x o x . . . . d o f o o o x o . . . 15
14 . x x x . . . x o o o x o . x x x . . 14
13 . . . . . . . . x o x x o . . . o o . 13
12 . o o x . x . x . x . x o . o o o x . 12
11 . . . . o o x x . x . x o o x o x x . 11
10 . x x x x x o x . . x . x o x x x . . 10
09 . o o x o . o . o o x x x o o x x o . 09
08 . . o o o . o . o . o o x o x . . x o 08
07 . . . . . . . x x o . x o o x x x o . 07
06 . . x x x o o o o o . o . . x o o . . 06
05 . . . . o x x x x o x . . g x o . o . 05
04 . . . . o o x . x x . x . x e x o . . 04
03 . . . x x x o x x o x . x . x c x o . 03
02 . . . . . . o o o o o o o x . b a . . 02
01 . . . . . . . . . . . . . . . . . . . 01
   a b c d e f g h j k l m n o p q r s t 

At this point, the situation in the game looks pretty well decided; we're into yose, or endgame. What ends up happening, though, is a huge furikawari. White plays "a" and puts Black in atari. Rather than connecting at "c" and letting White destroy territory along the edge, Black allows a ko by playing "b." White takes the ko at "c" and Black makes his first threat at "d," threatening to capture five White stones. White ignores the threat and captures at e. Black must follow through on his threat (or else it wasn't a threat to begin with), so Black captures at f. White cuts at g, and the real fun begins. Let's look at how the board looks now:

   a b c d e f g h j k l m n o p q r s t 
19 . . . . o x x . . . . . . . . . . . . 19
18 o o . o . o x . . x . x . . x x o . . 18
17 x o . o . o x . . . x o . x . . o . . 17
16 x o o . . x x . x x o o . x o o . o . 16
15 x x o x . . . . x . x o o o x o . . . 15
14 . x x x . . . x . . . x o . x x x . . 14
13 . . . . c . . . x . x x o . . . o o . 13
12 . o o x b x . x . x . x o . o o o x . 12
11 . . . . o o x x . x . x o o x o x x . 11
10 . x x x x x o x . . x . x o x x x . . 10
09 . o o x o d o . o o x x x o o x x o . 09
08 . . o o o . o . o . o o x o x . . x o 08
07 . . . . . . . x x o . x o o x x x o . 07
06 . . x x x o o o o o . o . . x o o . . 06
05 . . . . o x x x x o x . . o x o . o . 05
04 . . . . o o x . x x . x . x o a o . . 04
03 . . . x x x o x x o x . x . x o . o . 03
02 . . . . . . o o o o o o o x . x o . . 02
01 . . . . . . . . . . . . . . . . . . . 01
   a b c d e f g h j k l m n o p q r s t 

Black has picked up five stones, but now there's a new ko at q4, and if Black loses it, all his stones on the right die, due to the White cut at o5. Black captures the ko at "a," and White threatens at "b." Black would lose a lot on the left side if he ignored this, so he answers at c. White recaptures the ko (at "a" again), and it's Black's turn to threaten. Black should actually begin with local threats, like o6 (threatening to capture the cutting stone, so he'd live if White filled the ko now), but he's not thinking properly, so he threatens elsewhere, at "d". White decides to ignore it and fills the ko. Black follows through his threat and finishes cutting at "e," killing the White stones on the left, in return for his on the right. Let's look at the board again, removing the dead stones (even though they aren't actually captured yet) so that it's easy to see where the new territory lines are:

   a b c d e f g h j k l m n o p q r s t
19 . . . . o x x . . . . . . . . . . . . 19
18 o o . o . o x . . x . x . . x x o . . 18
17 x o . o . o x . . . x o . x . . o . . 17
16 x o o . . x x . x x o o . x o o . o . 16
15 x x o x . . . . x . x o o o . o . . . 15
14 . x x x . . . x . . . x o . . . . . . 14
13 . . . . x . . . x . x x o . . . o o . 13
12 . . . x . x . x . x . x o . o o o . . 12
11 . . . . . . x x . x . x o o . o . . . 11
10 . x x x x x o x . . x . x o . . . . . 10
09 . . . x . x o . o o x x x o o . . o . 09
08 . . . . . x o . o . o o x o . . . . o 08
07 . . . . x o . . . o . x o o . . . o . 07
06 . . x x x o o o o o . o . o . o o . . 06
05 . . . . . x x x x o x . x o . o . o . 05
04 . . . . . . x . x x . x . x o o o . . 04
03 . . . x x x o x x o x . x . x o . o . 03
02 . . . . . . o o o o o o o x . x o . . 02
01 . . . . . . . . . . . . . . . . . . . 01
   a b c d e f g h j k l m n o p q r s t 

The whole right of the board is now White, and the whole left is Black. It should be clear that a massive exchange of territory has taken place. It will be left to the diligent reader to determine who this furikawari benefitted more (because I haven't calculated it myself), but for those interested, the result of the game was that Black (me) won by 8 points before komi.

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