is to move your pieces around the game board, past your opponent's pieces, and off the board
before your opponent
does the same in the opposite direction. Four distinct strategies
have evolved to do this in standard Western
backgammon. For discussion of other types of backgammon games, see Tavli
But before I proceed, here's the single most important thing to know about backgammon:
Luck has almost no influence on the outcome. Certainly, an unfortunate roll or string of rolls can cost you a game. But a game usually consists of several dozen rolls and even over that short a period luck begins to even out, and over the course of a whole evening the player who calculates probabilities best will always win. Because of the uncertainty of any given roll, planning your game is futile, but intelligent reaction and response to the fluid shifting of position are anything but. Devotees understand this, and rarely play single games, but rather series of five games or more, sometimes much more.
The running game
The running game strategy is all about speed. Pieces are moved as far and as fast as possible with due regard for not getting hit but little or no attention to blocking. Getting one's pieces into the inner board and bearing them off is all that matters. When the dice are with you it seems effortless, but the running game is vulnerable to all the strategies that involve blocking and hitting. Used primarily by beginners and the unusually lucky.
The blocking game
Similar to the running game, but with attempts to interfere with your opponent's progress as you move your own pieces. For example, on a roll of doubles you might move two pieces together rather than a single piece twice as far, thus creating a blocking anchor. Or rather than moving a blot to safety, you might cover it instead, also creating an anchor. Otherwise, still focused on getting out fast.
The priming game
A prime is a block of six contiguous points with two or more pieces on them, which blocks any of the opposing player's pieces behind the prime from crossing and escaping. The priming game is superficially similar to the blocking game, but instead of just slowing the opponent down, primes are set up to actually force him to make moves that damage his own position or allow him to get hit. The ultimate goal of the priming game is to get your opponent on the bar behind a prime in your inner board. From this position your game is essentially won, because until you clear a space in your inner board, your opponent doesn't even get to roll the dice as you move your pieces and roll again. Even if you can't manage an inside prime, outside primes still block your opponent completely and force him to waste rolls or break up his position, making it easier for you to reenter if hit and so allowing you to take even more chances moving and extending your prime. Leverage, in a word.
The back game
The name of the game. Most sophisticated and difficult of the strategies, the back game works by deliberately getting your pieces hit and sent back into your opponent's inner board. This does two things for you: it gives you unassailable anchors in his inner board on which you can reenter without delay, allowing you to be hit with impunity and therefore to put blots where they can do the most good building your prime. Second, those points you hold in your opponent's inner board seriously hamper his ability to bear his pieces off safely and get out of the game. When you play a back game you ignore falling numerically way behind and snatch victory from the jaws of defeat by hitting your opponent's pieces just before they are taken off the board. At a minimum five or six pieces must be hit and sent back, because you'll need four to make two anchors and another piece or two to hit his blots as they become exposed trying to bear off. After you have set your anchors you can kill time by continuously getting hit and reentering, while using spare rolls to set up a prime near or in your inner board. Ideally you close your inside prime just as your opponent has to break up an anchor in his inner board, leaving vulnerable pieces. Your multiple anchors in his inner board give you good odds to hit those pieces, and with him then stuck on the bar he's locked out of play as you move your remaining pieces around the board and begin to bear off. Even if he reenters as soon as you reopen your inner board, his piece still has to travel all around the board as you continue to bear pieces off. With a bit of luck, your opponent will not manage to reenter as soon as you open up, leaving him even further behind you and opening up the possibility of a gammon, or better. A most satisfactory outcome.