There are quite a few differences between the two different sets of snooker rules. It is important to know the differences if you have any intention of playing both versions at some point. Since most of the world plays by the international rules and the game is more popular outside of the United States, chances are good that at some point, you will need to know the international rules if you want to play the game.
You might have a tough time finding a snooker table in an American pool hall since it really is not played very much in the United States — so learning the international rules will help you play the game when you travel to other countries.
Following are the major differences between the American and international rules:
The break: In the American rules the pink ball is frozen to the apex of the racked balls, while the international rules state that the pink ball should not touch the apex ball. Also on the break shot, the American rules state that you must either pocket a red ball or a red ball and the cue ball must touch a cushion (otherwise it's a foul).
Foul penalties: The international version says a foul penalty is worth between 4 and 7 points, while the American rules say that a foul is 7 points. In the international game, if you foul, your opponent receives either 4 points or the value of the on-ball (whichever is highest).
Free ball: In international snooker there is a “free ball” rule that does not exist in the American rules. A free ball means that if the cue ball is snookered after a foul is committed, the player who snookered may call a shot (which is not the on-ball) and that ball becomes the ball for that shot.
The “miss” rule: The international rules say you must strike the on-ball to the best of your ability, but if the referee decides you haven't, your opponent can ask that you strike again with all balls relocated to their original positions. There is no such rule in the American version.
Touching ball rule: Again this rule applies only to the international rules. If the cue ball is frozen to the on-ball, the referee can say “ball touching” and the player must shoot away from the on-ball (not at the on-ball).