Black – Pips 135 (-44)
Black to Play 6-4
In this game Black launched a blitz after a few moves were made on both sides, and now White is in serious trouble with two men up in the air facing a four-point board with more blots floating around. Black’s 6-4 gives him several excellent options; his job now is not to get too excited, but to just find the most efficient way to bring the game home.
In this position Black has three goals. Without trying to assess their relative importance, here they are:
(1) Close the 5-point. Closing the ace-point would also be nice, but Black won’t have the ammunition in place to do that for some time. With a small double, he’ll cheerfully switch points, but otherwise the ace-point will have to wait. (The most likely outcome of this position is in fact a well-timed ace-point game.)
(2) Pick up blots. Hitting more blots helps in several ways. The extra blots hit obviously lead to both more gammons and more backgammons. Hitting more blots also buys time to escape the back checkers before White can get everybody in from the bar. Finally, hitting blots eliminates potential builders and slows down White’s ability to put his position back together once he enters.
(3) Escape the back checkers. The sooner Black can extricate his back checkers, the sooner he avoids a potential disaster scenario: White enters both checkers from the bar, and Black is caught with blots in the outfield to pick up as well as refugees in White’s inner board that need to get out quickly.
Now let’s look at Black’s possible plays. He has a bunch, some of which emphasize one goal only, while others are more balanced.
Play A: 21/17* 24/18: The “Get-out-of-Dodge” play, this strongly favors escaping and hitting. Black picks up one blot now while generating a double shot at the last outfield blot.
Play B: 13/7 13/9: This “Close-him-out-quick” play ignores the blots while creating three builders for the 5-point, as well as some numbers which might be used to hit on the ace-point if White fans.
Play C: 24/14*: This play hits the blot that’s hardest to hit, while escaping the checker that’s hardest to escape.
Play D: 21/17*/11: Hit-and-Build #1 puts a third checker up while creating another builder for the 5-point.
Play E: 21/17* 13/7: Hit-and-Build #2 creates a different builder for the 5-point which also shoots at the ace-point. In addition, Black still has a direct shot at the blot on the 14-point.
Before we discuss the merits of the three approaches, we can prune our list a bit. It’s pretty clear that Play E, with a builder on the 7-point, dominates Play D, which puts a builder on the 11-point. The builder on the 7-point not only aims at the 5-point but also aims at the ace-point, while serving as a slot for the bar if White starts to enter and Black decides he needs a prime. So we can eliminate play D.
Now let’s compare Play A and Play C. Both involve 24/18. Do we then prefer 18/14* or 21/17*? Since neither play puts a builder in position for the 5-point, 21/17* looks better, escaping a checker and getting some additional shots. So we’ll drop play C from our list of candidates.
With those two eliminations, we’ve reduced our list of possibilities to three: Play A, the best for escaping the back men; Play B, the best for closing the 5-point; and Play E, the best for making progress on both fronts. Now what?
In the pre-bot era, the standard play here was Play B, 13/7 13/9. The idea was that closing the 5-point was crucial, after which Black could pick up the blots at his leisure. While playing two checkers down didn’t actually give that many new numbers for closing the 5-point, it did make Black a big favorite to hit loose if White entered, after which White would be an underdog to hit back, while Black would then have multiple cover numbers if White missed. In a high-stakes chouette in the 1980s or 1990s, this play wouldn’t even have generated much discussion — with two on the bar, building the board quickly was thought to be paramount.
One of the first lessons we learned from the early bots was that hitting was a big deal no matter how many men were on the bar. Every blot hit represented more gammons won, and if the gammon was in the bag then each blot hit started increasing the backgammon count. The problem with building plays is that blots are never as easy to hit as they appear to be. If you have a hit now but you pass on the hit to make a structural play, you may never get another chance to hit. In this problem, for instance, bringing down more builders is always trivially easy, but hitting never will be.
If we eliminate the building play and focus on the two hits, then 21/17* 13/7 dominates 21/17* 24/18. While we don’t want to sacrifice hitting for building, we also can’t ignore building, because our life will get a lot easier if we prevent White from making our 5-point. In addition, a blot on the 7-point is a fabulous multi-purpose blot: it’s simultaneously a builder for the 5-point, an attacker for the ace-point, and a slot in case White makes our ace-point and we need the bar-point for control.
To see the power of hitting, take a look at the wins/gammons distribution after an Extreme Gammon rollout:
– Overall G/BG
– Win % Win %
21/17* 13/7 79.5 63.6
21/17* 24/18 79.1 62.2
21/17*/11 79.2 60.6
24/14* 78.8 61.0
13/7 13/9 78.2 60.7
Although the numbers are relatively close, notice that the non-hitting play scores lowest in overall winning percentage and almost tied for last in gammon/backgammon percentage. Hitting is the road to winning more gammons, which is fairly obvious; but it’s also the road to winning more games, by keeping White on the bar longer allowing Black to get his army home.
How do things change if Black is closer to getting home? Take a look at these three related positions.
Black – Pips 121 (-58)
Black to Play 6-4
In (B), we’ve moved Black’s rear checker from his 24-point around to his 10-point. Black’s game is now much stronger, both because he’s closer to closing his 5-point, and he doesn’t need to worry about escaping the back checker. How does this change the relationship between 13/7 13/9 and 21/17* 13/7?
Actually, it makes the hitting play stronger! With only one checker back, hitting anybody has become relatively more difficult, so the value of hitting has risen. And as the number of checkers aimed at the 5-point rises, the relative value of adding yet another builder shrinks. So 21/17* 13/7 now dominates 13/7 13/9 by an even wider margin.
Black – Pips 114 (-65)
Black to Play 6-4
The trend continues in (C), where we’ve moved a checker from Black’s midpoint to his 6-point. Now 13/7 will put a fourth builder in place, so the gain from a fifth builder (with 13/9) is tiny. Once again 21/17* 13/7 is right, and both 21/17*/11 and 13/7 13/9 are big blunders.
Black – Pips 112 (-67)
Black to Play 6-4
If we move enough checkers around, eventually new ideas start to appear. Here we’ve put another checker in place, on Black’s 11-point. Once again, 21/17* 13/7 dominates two down, as we expect. But now a new contender rises from the ashes. Hitting on the ace-point with 11/1* now beats out 21/17* 13/7 for top place. The value of preventing White from establishing any anchor is huge as long as there are cover numbers in place.
