Blocking in Backgammon: Points, Primes and Closed Boards

Blocking is one of the two big ideas in backgammon, alongside racing. Instead of simply running home, you build a wall of points in front of your opponent's checkers so they cannot get past. A strong block can win a game even when you are behind in the race, because your opponent's trapped checkers are not going anywhere.

Why Points Block

A point held by two or more of your checkers is closed to your opponent: he cannot land there. One closed point is a minor obstacle. Several closed points in a row become a real barrier, because a checker needs an open landing spot within reach of its dice to move forward.

So the basic rule of blocking is: make points next to each other. Three points in a row block more than three scattered ones, because they leave fewer landing spots in the stretch your opponent has to cross.

The Prime

A prime is a row of consecutive made points. The longer the row, the harder it is to pass:

• A four-point prime blocks many rolls but can still be jumped with the right numbers.
• A five-point prime leaves only a few escaping rolls.
• A six-prime, six made points in a row, is a complete wall. No single die can move more than six pips, and every landing spot within six pips is closed, so a checker directly behind a six-prime cannot escape at all.

Here is an example. Suppose you hold your 4, 5, 6, 7, 8 and 9 points, and one of your opponent's checkers sits on your 3 point, directly behind that wall. Whatever he rolls, that checker stays where it is until you break the prime. Meanwhile his other checkers must keep moving, and his position may crumble while he waits.

A gap in the row is sometimes called a broken prime. It is weaker, because the gap gives your opponent a place to land and then jump the rest.

Where to Build the Block

Points in your home board help when your opponent has checkers on the bar, but they do nothing against checkers that are already past them. Points in your outer board, especially your bar point (7) and 8 point, block checkers that are still trying to escape from your home board. The strongest primes usually run across the middle: from around your 4 or 5 point up to your 8 or 9 point.

Your 5 point and your bar point are the two most important blocking points to make early in the game.

Building a Prime Step by Step

• Bring builders into range. Builders are spare checkers within six pips of the point you want to make. The more builders you have, the more rolls make a new point.
• Keep your checkers together. Move them as a group rather than sending one far ahead, so they can combine to make points.
• Slot when it is safe enough. Putting a single checker on a key point, planning to cover it next turn, is a fast way to build, as long as the risk of being hit is acceptable.

Rolling the Prime

A prime is not fixed in place. If your opponent's checker is trapped and you need to move forward, you can "roll" the prime: make a new point at the front while releasing the one at the back. Done carefully, this walks the wall toward your home board with the trapped checker still behind it, until it becomes a closed board.

Closing Your Home Board

When you hold all six points in your home board, it is closed. A hit checker cannot enter at all, and your opponent loses his turns until you open a point. The more points you hold, the harder it is to come in:

What a Strong Block Is Worth

A player with a full prime and an opponent trapped behind it is usually a big favorite, and often has good chances to win a gammon. In match play this is the kind of position where a doubling cube decision comes up. To see how blocking fits with the rest of your game plan, read basic strategy and backgame advice, which looks at the same walls from the defender's side.