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Quiz and Lesson of the Week/By Phil Simborg and Perry Gartner











As you can see from the rollout below, the correct play is to make the 5 point.  Scroll down for commentary from myself and Perry.



And now for some commentary:

 

The candidate plays, 9/6 9/8, 6/2, and 8/5 6/5, represent 3 different levels of aggression. Let’s look at them:

9/6 9/8
Black has a prime formation, albeit gapped. The prime is preventing White from making an easy escape. The other side of the coin is the prime has the potential for White getting a shot at a blot as the prime breaks down during the bear-in. Black can avoid leaving a shot on the 9 point by clearing now. Black still has the option of attaching if White springs one loose, but needs to be more careful about leaving its own blots without the 9 point intact. Black is giving up its most potent builder and blocker when breaking from 6 away. Giving up one of 4 builders reduces the pointing numbers from 16 to 9, and lessens the remaining hitting numbers by 5. This is the most conservative approach.

6/2
This play maintains the prime, advances 4 pips while giving up one of two potential builders or hitters now on the 6 point. White must run one with a 4(except 4-4 and 2-2 run 2) , 2-5, or 2-6. If White rolls one of these anchor breaking number, Black can point, hit and pass, or hit loose with everything but double 4. Look at how breaking the anchor with 4-1 and 4-2 plays.

This move says White escaping and winning the race is big enough to justify the risk of blotting later on the 9 or 8. The move picks up more gammons and wins more races than the first play we considered because when White rolls one of the 15/36 numbers that do leave, having the 9 point offers more firepower and blocking power aimed at the remaining blot. Putting White on the roof slows White down, and keeping White on the roof for a roll or 2 makes a huge difference in the race. Black is a favorite to make the 3 point before White can enter and escape but is an underdog to make the 5 before White enters and escapes. Without the 5 point, the bear-off is slowed, and gammons are harder to come by, but no voluntary blot is out there. This is a more risky approach but still treading water compared to the third play.


8/5 6/5
Only one more point to closeout and awesome firepower aimed at it if White were to leave a blot on the 3 point on the next roll.

Just how bad is it for Black to get hit on the 8 point? Unless White hits with 5-5, and 5-4, only one checker pops into the outfield. Look at the incoming immediate returns on the 3 point from the roof. If the cube were in the middle with Black on the roof it would be a pass from the middle for White. If Black doesn’t hit back immediately it looks like there will be multiple shots in most of these variations. Even 5-4, and 5-5, don’t have a comfortable ride home.

When White doesn’t break anchor,16/36, the made 5 creates another landing spot for Black’s outfield checkers, lessening Black’s blotting numbers, and the 5 is transformed into a point where useful builders or spares can end up. Closing the gap on the 5 also improves Blacks race for gammons and even single wins in some scenarios.

A closeout of one checker with another in the outfield (depending where it is and what points the spares are on in the inner board), wins 94% to 98%, with 9%-14% gammons. You can readily see why you don’t want to steer this game into a pure race where you won’t win anything close to the numbers that come from contact. As an exercise I simulated a race from this position without contact on either side and found White won 29% of these races.

Making the 5 point achieves a close-out more often than the other plays, and wins more single games as well as more gammons. A 5 point board combined with builders in position for the 6th, turn out to seriously out- weight the cost of getting hit. Constraining one checker with 2 open points is just so much harder to do.

This is the most aggressive of the plays, encouraging a showdown sooner than later.



Snowie
Snowie has 8/5 6/5 winning 80%, with 13% gammons compared to 76% wins and 6% gammons for the 2nd best play, 6/2. The third play wins 73% with 4% gammons.

[All percentages given are rounded] [Snowie Rollouts are level 2, precise, 648 games]





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