A Big Defensive Hammer — How to Wield It Effectively
Paul Magriel, 1979
New York Times, January 25, 1979
Backgammon The modern trend in backgammon is to emphasize the attacking game. In many situations, however, attack is not possible, and winning requires precise defense.

The most important points to own are defensive points in or adjacent to your opponent’s home board. The best of these, in order of importance, are the 20-point, 21-point, and 18-point. These points, called “advanced anchors,” provide a good measure of security. Holding merely a single one of them gives a significant amount of protection against being closed out or primed.

In the diagrammed position, White has escaped with both of his back men and is clearly far ahead in the race. Consequently, Black must set up his best possible defensive formation in hopes of getting a shot and hitting White.

Black to play 4-1.
With the roll of 4-1, the obvious play is bar/20, reentering and making the 20-point. This seemingly natural play is, in fact, a serious error. Because Black already holds the 18-point, he has no pressing need for the additional security provided by the 20-point. The drawback to holding both the 18- and the 20-points is that it is impossible for White to leave a shot immediately. More important, White has good prospects for bypassing both these points without ever leaving a shot — he can safely handle any awkward roll by playing behind Black.
(a) bar/20
(b) bar/24, 20/16
The correct play is bar/24, 20/16. The key decision is to keep a man back on the 24-point, restricting White’s movement in order to force White to leave a shot. This man single-handedly patrols all the open points in White’s home board. White cannot now land with a blot on the 24-, 23-, 22-, or 20-points without being exposed to a direct shot. Because of Black’s excellent coverage of these points it will be exceedingly difficult for White to come home safely.

With the 1, Black reenters and stays on the 24-point. The best way to complete the play is to use the 4 to bring a man out to White’s 16-point. Even though this man is now exposed to a triple shot, White gains nothing by hitting Black on the 16-point. By contrast, if Black leaves a single man on the 20-point White may profitably point on Black — possibly using the men on the 14- or 15-point.

Most players reason that if holding one advanced anchor is good, then two would be even better. Paradoxically, this is hardly ever the case in practice. The best players, in fact, often go out of their way to avoid holding two advanced anchors. Such a configuration makes inefficient use of your men. In addition, it is a burden to hold both for any length of time.

XG logo
Tom Keith 2013 
Money play
Centered cube
Black rolls 4-1

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

4-1: Game BG   Equity
1 bar/20 W
−0.7352 x  (a)
2 bar/24, 20/16 W
−0.9594 (0.2242)  (b)

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