Knowing the Exact Position Helps in Deciding on Tactics
Paul Magriel, 1980
New York Times, June 8, 1980
Backgammon The fourth annual Plimpton Cup for the World Amateur Backgammon Championship will be held this week, Tuesday to Sunday, in Las Vegas, Nev. The popularity of this event is due in no small part to the $100,000 first prize.

Prizes this substantial are rare in any sport or game, and are usually available only to the top professionals. The Plimpton Cup, however, is restricted to amateurs — professional players must compete in a separate “open” event. The caliber of play is not as high in the amateur event, but the competition is fierce.

Under pressure, amateurs are more prone than professionals to commit errors. In particular, near the end of a long match, amateurs often neglect the subtleties of match play that never arise in nontournament play. The exact score of the match influences not only the doubling strategy but also the play of the checkers.

Black to play 6-6.
The diagrammed position, taken from the third Plimpton Cup, shows how failure to monitor the match score can be costly. Black won the previous game to go ahead 10–9 in an 11-point match. When Black reached match-point, 1 point from victory, the Crawford rule went into effect. This rule prohibits White from doubling for one game but does not prevent White from winning a gammon (or double game), worth 2 points.

With the roll of 6-6, Black’s hopes for winning this game were suddenly revived. Black saw that the race was now quite close and decided to play 21/15(2), 21/9, moving all three of his back men out of White’s home board and continuing one man to the 9-point. Although this gives White a direct 2-shot (12 chances out of 36), Black was willing to take this risk in order to increase the likelihood of winning the game. He reasoned that clearing the 21-point immediately would give him the best chance to avoid any later contact with White, and so enable him to enter a pure running game.

(a) 21/15(2), 21/9

In the actual game, Black’s play turned out disastrously. White rolled a 2 and hit Black’s blot on the 9-point. Black, with his anemic home board, could offer no resistance and was soon closed out with four men still stranded in White’s outer board. Because of these outside men, Black was unable to escape a gammon and so lost not only the game but the match.

Black went wrong because he neglected to examine the exact match score. As a result, he chose the play that gave him the best chance to win the game — but not the match! To see why, examine what White needs to win this 11-point match with Black ahead 10–9.

Because White cannot double, he must either win 2 games in a row or else win a gammon. In other words, Black can lose the first game and still have a 50–50 chance to win the match. Thus, with the score 10–9, Black has two basic objectives — winning the game and avoiding a gammon. Black cannot afford to go all out to win this game if it significantly increases his chance of being gammoned and so jeopardizes the whole match.

(b) 21/9, 14/8(2)

Black can almost eliminate the possibility of being gammoned by maintaining his anchor in White’s home board on the 21-point. The obvious way to do this is 14/2(2), making the 2-point. The drawback to this play is that Black gives up all flexibility and will probably be forced to run off the 21-point with one man next turn.

The best play is 21/9, 14/8(2). With this unusual move, Black strengthens his winning chances while simultaneously keeping the chance of being gammoned to a minimum. Even though Black gives White a direct 2-shot, he doesn’t fear losing a double game because he retains his anchor. If White misses, Black will have better winning chances than with the conservative 14/2(2): Black’s moves will be much less forced and he will be able to start rebuilding his home board while waiting for the right time to move off the 21-point.

*  *  *

Information about the Plimpton Cup can be obtained from the American Backgammon Championships at 575 Madison Avenue (486-1489). Entries will also be accepted in Las Vegas from Tuesday to Friday of this week.

XG logo
Tom Keith 2013 
Match to 11
White 9, Black 10
Black rolls 6-6

1296 games with VR
Checker play: 2-ply
Cube play: 3-ply Red

6-6: Game BG   Equity
1 21/9, 14/8(2) W
−0.8527 x  (b)
2 14/2(2) W
−0.9271 (0.0744) 
3 21/15(2), 21/9 W
−1.1067 (0.2540)  (a)

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