Strategy--Checker play

Forum Archive : Strategy--Checker play

Splitting your back men

From:   David Montgomery
Date:   23 June 1995
Subject:   Re: Splitting in a priming game
Google:   3sf4gm$

USRobots writes:
>  24  23  22  21  20  19      18  17  16  15  14  13
> -----------------------------------------------------
> | O               X   X |   |     X   X       X   O |
> | O               X   X |   |     X               O |
> |                 X   X |   |     X                 |
> |                     X |   |     X                 |
> |                       |   |                       |
> |                       |   |                       |
> |                     O |   |                       |
> | X       O       O   O |   |     O                 |
> | X       O       O   O |   |     O       O   O     |
> |_______________________|___|_______________________|
>   1   2   3   4   5   6       7   8   9  10  11  12
> score -3:-3, cube=1, pip count: O-145, X-139
> O to play 2-1
> [ USRobots played 13/11 24/23 ]
> 1.) Was my actual move the best?

There are so many possibilities here that look plausible
that I would not expect to find the best move over the board.
In fact, sometimes in positions like this I can't find the
right move using rollouts until I've looked at if for a
couple of months, since the best move may not occur to me at first.

My first reaction is to play 24/23 10/8.  I think this is
better than 24/23 13/11 because:

1) The 11 point is not such a valuable point, being 6 away
   from the 5 point.  The midpoint isn't vital either, but
   I think since it provides better coverage of the outfield
   and blocks 6-6, it is a slightly better point to own.
2) 10/8 leaves only 1 outfield blot, subject to 2 hits (6-4),
   while 13/11 leaves 2 outfield blots, subject to 4 hits
   (6-3, 6-6, 3-3) of which two are tremendous rolls for X.
3) The fact that 10/8 removes a builder 6 away from the 4
   point is not that significant because O has a lot of uses
   for sixes already, either running or making the bar point
   or even making the two point.

> If not [best], was it at least close, or was it clearly inferior?

In my opinion, it is close.  It looks a little worse to me, but
not by much.

> 2.) What features of a priming game are most important when one is
> deciding whether to split one's runners?  Magriel's "Backgammon" merely
> states that such decisions are very difficult, while Robertie's "Advanced
> Backgammon" doesn't seem to cover the issue at all.

Whenever you split your back checkers, a principle consideration
is how strong your opponent's attack is likely to be.  This is
primarily determined by
1) your ability to defend yourself, which is determined by
    A) whether you have an anchor
    B) how many blots you have about the board and how vulnerable they are
    C) how loose your opponent's position is (i.e., whether you are
       likely to be able to return hit ).
    D) how strong your offense is, since a strong offense may
       deter your opponent from a full-fledged attack.
2) your opponent's ability to build a strong board, which is determined by
    A) how strong the opponent's board is all ready
    B) how much and how readily material is available for building
       new points.
3) your opponent's ability to come home after a successful attack.
    For example, if you have your opponent primed, then your opponent
    will never be able to come home after attacking you.  Even if
    you have a 4 or 5 prime, the opponent's attack may temporarily
    succeed, but then fall apart because of an inability to free
    the back checkers.

The above I think applies quite generally.  In priming games,
the additional consideration of note is timing.  If you will have
great difficulty extracting your rear checkers, and you have significantly
less timing than your opponent, then splitting is very often called for
even in the face of a potentially strong attack by the opponent.  By
splitting you hope to gain timing in three ways:
        A) the actual movement of the back checkers are pips that you
           avoid moving on the offensive side.
        B) if you can escape a back checker, you usually pick up about
           two rolls worth of timing.
        C) if you are hit, you move backwards, and you may gain even
           more timing due to fanning.
On the other hand, you may just get closed out and backgammoned :-).
But if you have a strong prime you hope that category 3) above will
give you good winnning chances even when attacked.

On the other hand, if you will probably not have such great difficulty
escaping the back checkers (and your opponent will), and you have more
timing than your opponent, then there is no need to split.  Just contain
the opponent, wait for his or her prime and board to bust to splinters,
come around (maybe trapping the opponent off his or her anchor while
you're at it) and win a backgammon :-).

In between is a huge gray area.

In the given position, I don't think priming considerations give
any great motivation for splitting.  O looks to have the better timing,
by just a bit.  Since the opponent's bar point is open, O should have
escaping chances for some time.  Even if X closes the bar, X will only
have a four prime, and O will probably be able to split to the 22 or
21 points if necessary.  For all these reasons, I'm not 100% convinced
that splitting is correct, although I would do it.

For me the split is motivated by the fact that O's prime is not so
strong either.  With the bar point open, X may be able run to a checker
out and gain both a timing advantage and the advantage of having one
less checker back.  It may turn out that neither side ever fully
primes the opponent, and the advantage in this case is likely to be
with the player that can escape a checker.  By splitting, O increases
the likelihood of being this player, as well as getting more fly
shots at X's outer board blots.  X has a lot of material ready for
an attack, but currently has only a two point board, so I think that
the blitz is only a small danger.

> 3.) (Bonus question) What are the backgammon chances with four checkers
> closed out?

I don't know.  I'm sure I've seen this rolled out somewhere though --
I think in _Fascinating_Backgammon_.  If no one else posts this I'll
look it up.

> Thanks for any input,
> USRobots

David Montgomery
monty on FIBS
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Strategy--Checker play

Avoiding major oversights  (Chuck Bower+, Mar 2008) 
Bearing off with contact  (Walter Trice, Dec 1999) 
Bearing off with contact  (Daniel Murphy, Mar 1998)  [Long message]
Blitzing strategy  (Michael J. Zehr, July 1997) 
Blitzing strategy  (Fredrik Dahl, July 1997) 
Blitzing technique  (Albert Silver+, July 2003)  [GammOnLine forum]
Breaking anchor  (abc, Mar 2004) 
Breaking contact  (Alan Webb+, Oct 1999) 
Coming under the gun  (Kit Woolsey, July 1996) 
Common errors  (David Levy, Oct 2009) 
Containment positions  (Brian Sheppard, July 1998) 
Coup Classique  (Paul Epstein+, Dec 2006) 
Cube ownership considerations  (Kit Woolsey, Apr 1996) 
Cube-influenced checker play  (Rew Francis+, Apr 2003)  [GammOnLine forum]
Defending against a blitz  (Michael J. Zehr, Jan 1995) 
Estimating in volatile situations  (Kit Woolsey, Mar 1997) 
Gammonish positions  (Michael Manolios, Nov 1999) 
Golden point  (Henry Logan+, Nov 2002) 
Hitting loose in your home board  (Douglas Zare, June 2000) 
Holding games  (Casual_Observer, Jan 1999)  [Long message]
How to trap an anchor  (Timothy Chow+, Apr 2010) 
Jacoby rule consideration  (Ron Karr, Nov 1996) 
Kamikaze plays  (christian munk-christensen+, Nov 2010) 
Kleinman Count for bringing checkers home  (Øystein Johansen, Feb 2001) 
Late loose hits  (Douglas Zare+, Aug 2007)  [GammOnLine forum]
Mutual holding game  (Ron Karr, Dec 1996) 
Pay now or pay later?  (Stuart Katz, MD, Nov 1997) 
Pay now or pay later?  (Stephen Turner, Mar 1997) 
Pay now or play later?  (Hank Youngerman+, Sept 1998) 
Play versus a novice  (Courtney S Foster+, Apr 2004)  [GammOnLine forum]
Playing doublets  (Grunty, Jan 2008) 
Playing when opponent has one man back  (Kit Woolsey, May 1995) 
Prime versus prime  (Albert Silver+, Aug 2006)  [GammOnLine forum]
Prime versus prime  (Michael J. Zehr, Mar 1996) 
Saving gammon  (Bill Riles, Oct 2009) 
Saving gammon  (Ron Karr, Dec 1997) 
Splitting your back men  (KL Gerber+, Nov 2002) 
Splitting your back men  (David Montgomery, June 1995) 
Trap play problem  (Brian Sheppard, Feb 1997) 
When in doubt  (Stick+, Apr 2011) 
When to run the last checker  (Stick Rice+, Jan 2009) 
When you can't decide  (John O'Hagan, Oct 2009) 

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