Playing against eXtreme Gammon in a match I got this position playing white:



My thinking was that if I let black checker on 9 escape I am losing the race so I need to maximize the chances of catching it. I thought that taking 13 point prevents 13 being hit and I don't mind being hit on 19 that much as I will get a chance to re-enter hitting black.

Yet 19-13 is a huge blunder. The correct move looks very counter-intuitive to me. How should I think about this situation to arrive at the correct move?

You need to hit and contain black’s straggler. To do so, you want to maximize your chances of hitting. Since you missed with this roll you need to maximize you chances for the next roll and for subsequent ones. Even if black manages to get his straggler to safety, he’s still got an inflexible board with an outfield point to break. Chances are he will leave a shot - might as well make it a double shot; hence 19-18. Once you split the 19 point, you no longer want that blot on the 13. A double hit on the two outfield blots leaves only a 3 to renter and hit and gives black a better chance to scramble home.

Think of how some of your opponent’s rolls play. For example, with 64 and your play he plays 9-15 16/20. You have only 3s to hit. With the correct move, black would play 9/19* or possibly 9/15 16/20. Either way two numbers hit (3s and 6s or 3s and 4s). You maximize your hitting chances with the correct play.

Besides keeping the 13 to block 4s doesn’t really help much. 24 and 44 are the only rolls where the straggler can’t move. With 24 he probably covers the inner board blot and leaves the straggler put. With 44 he clears the outfield point and moves the straggler to the 13. You now have any 3 plus 65 and 54 to hit. Had you kept the 13 you’d have any 4 plus 31 and 22, one less roll, to hit.