Games: Backgammon

Chessplayers are used to the concept of zugzwang - where the player whose turn it is would prefer not to move at all as any move will weaken his position. In backgammon, zugzwang is not uncommon as a player will often have timing problems and would prefer to keep his position as it is.

The position above is an example of double zugzwang: whoever moves first will irreparably weaken his position. With Black on roll, his equity is approximately 0.38. With White on roll, Black's equity rises to 0.52. Black's ideal scenario would be that he could double in this position and then ask White to roll. In a money game with Black on roll he is not quite strong enough to double.

The position occurred in the Double Fives weekly tournament. In a match to seven points, Black trailed by three points to five. This match score is interesting. The trailing player should double if he has a good chance of winning a gammon. The leader needs only 20 per cent (rather than the normal 25 per cent) winning chances to take, provided there is not a huge gammon threat. After long thought, Julian Fetterlein, playing Black, doubled; and after even longer thought, The Doyen, playing White, dropped.

Both the double and the drop were correct. At 3-5 and with a reasonable gammon threat, this is an excellent pressure double. Although White will win 33 per cent of the time, this is offset by the number of gammons he loses when two or more of his men get closed out by Black. After all the arithmetic has been done, White's chances of winning the match are 59 per cent whether he takes or drops, so either option is acceptable.

This is an excellent example of how tournament and money play can differ. For money, Black should not yet double, but in a match, Black should double and White can drop.