Snooker is played on a rectangular table, 6 feet by 12 feet (about 1.83m by 3.66m), with six pockets, one at each corner and one in the middle of each long side. At one end of the table (the baulk end) is the so-called baulk line, which is 29 inches from the baulk cushion (the short cushion at the baulk end). A semicircle of radius 11½ inches, called the D, is drawn behind this line, centred on the middle of the line. The cushion on the other side of the table is known as the top cushion.
Because of the large size of regulation snooker tables, smaller tables are common in domestic situations and other situations where space is limited. These are often around 6 feet in length, and all the dimensions and markings are scaled down accordingly. The balls used are sometimes also scaled down, and/or reduced in number (in the case of the reds) such that the longest row of balls in the rack is omitted.
Snooker balls, like pool balls, are typically made of phenolic resin, but are smaller than regulation pool balls. Regulation snooker balls are 52.5 mm (approximately 2-1⁄8 inches) in diameter, though many sets are 52.4mm (2-1⁄16 in.) Some recreational sets are as large as 2-1⁄4 in., while miniature sets also exist, for half-size home tables. There are fifteen red balls, six "colour" balls (yellow, green, brown, blue, pink, and black), and one white cue ball. The red balls are not numbered, though the six colour balls often are, especially in the US, and can easily be mistaken at first glance for pool balls (the design is similar, but the numbering does not match pool's scheme).
At the beginning of a frame, the balls are set up in the arrangement shown. The six colours (a term referring to all balls but the white and the reds) are placed on their own spots. On the baulk line, looking up the table from the baulk end, the green ball is located where the "D" meets the line on the left, the brown ball in the middle of the line, and the yellow ball where the "D" meets the line on the right. This order is often remembered using the mnemonic God Bless You, the first letter of each word being the first letter of the three colours. At the exact centre of the table sits the blue ball. Further up the table is the pink ball, which sits midway between the blue spot and the top cushion, followed by the red balls, arranged in a tightly-packed triangle behind the pink (the apex must be as close as possible to the pink ball without touching it). Finally, the black ball is placed on a spot 12.75 inches from the top cushion.
The objective of the game of snooker is to strike the white cue ball with a cue in the direction of other object balls and to pot these object balls in one of the six pockets. This must be done according to the rules of the game, which are described below. By potting object balls points can be scored. The player who scores most points wins the frame, and the player who wins most frames wins the match.
A snooker match
A snooker match usually consists of an odd fixed number of frames. A frame begins with setting up the balls as described above. A frame ends when all balls are potted, or when one of the players concedes defeat because he is too far behind in score to equal or beat the score of the other player.
A match ends when one of the players has won the majority of the set number of frames and the other player can therefore not equal this. For example, when a match consists of 19 frames, the match ends when one of the players has reached 10 frames.
At the beginning of each frame the balls are set up by the referee as explained. This will be followed by a break-off shot, on which the players take turns. At the break-off, the white cue ball can be placed anywhere inside the D, although it is common for players to start by placing the ball on the line, between the brown ball and either the green or yellow ball.
Players take turns in visiting the table. When one player is at the table, the other cannot play. A break is the number of points scored by a player in one single visit to the table. A player's turn and break end when he fails to pot a ball, when he does something against the rules of the game, which is called a foul, or when a frame has ended.
When a player strikes the white, it can only first hit certain object balls. If the white first hits another ball, this is considered a foul. The ball or balls that can be hit first by the white in a certain stroke are called the ball(s) "on" for that particular stroke. The balls "on" are the only balls that can be potted by a player. The player receives points for this. If another ball is potted, this is considered a foul.
The game of snooker generally consists of two phases. The first phase is the situation in which there are still red balls on the table. In the first phase, at the beginning of a player's turn, the balls "on" are all remaining red balls. The player must therefore attempt to first hit and pot one or more red balls. For every red ball potted, the player will receive 1 point. When a red has been potted, it will stay off the table and the player can continue his break. If no red has been potted or a foul has been made, the other player will come into play.
In case one or more red balls have been potted, the player can continue his break. This time one of the six colours (yellow, green, brown, blue, pink and black) is the ball "on". Only one of these can be the ball "on" and the rules of the game state that a player must nominate his desired colour to the referee, although it is often clear which ball the striker is playing and it is not necessary to nominate.
When the nominated colour is potted, the player will be awarded the correct number of points (yellow, 2; green, 3; brown, 4; blue, 5; pink, 6; black, 7). The colour is then taken out of the pocket by the referee and placed on its original spot. If that spot is covered by another ball, the ball is placed on the highest available spot. If there is no available spot, it is placed as close to its own spot as possible in a direct line between that spot and the top cushion, without touching another ball. If there is no room this side of the spot, it will be placed as close to the spot as possible in a straight line towards the bottom cushion, without touching another ball.
Because only one of the colours is the ball "on", it is a foul to first hit multiple colours (and reds) at the same time, or pot more than one colour (or red).
If a player fails to pot a ball "on", it being a red or nominated colour, the other player will come into play and the balls "on" are always the reds, as long as there are still reds on the table.
The alternation between red balls and colours ends when all reds have been potted and a colour potted after the last red. All six colours have then to be potted in the correct order (yellow, green, brown, blue, pink, black). Each becomes the ball "on" in that order. During this phase, when potted, the colours stay down and are not replaced on the table, unless a foul is made when potting the colour and the colour is respotted.
When the colours have been potted, the frame is over and the player who has scored most points has won it (but see below for "The End of Frame" scenarios).
A foul is a shot or action by the striker which is against the rules of the game.
When a foul is made during a shot, the player's turn is ended and he will receive no points for the foul shot. The other player will receive penalty points.
Common fouls are:
first hitting a ball "not-on" with the cue ball
potting a ball "not-on"
potting the white (in-off)
hitting another ball than the white with the cue
making a ball land off the table
touching a ball with something else than the tip of the cue
playing a "push shot" - a shot where the cue, cue ball and object ball are in simultaneous contact
playing a "jump shot", which is where the cue ball leaves the bed of the table and jumps over a ball (even if touching it in the process) before first hitting another ball
playing a shot with both feet off the ground
Whereas in other games, such as pool, if the cue ball is touched with the tip of the cue when it is in baulk after being potted then a foul is committed, in snooker if the cue ball is touched with the tip after being potted and in the D, a foul is not committed as long as the referee is satisfied that the player was only positioning the ball, and not playing, or preparing to play, a shot.
When a foul is made, the other player will receive penalty points. Penalty points are at least 4 points and at most 7 points. The number of penalty points is the value of the ball "on", or any of the "foul" balls, whichever is highest. When more than one foul is made, the penalty is not the added total — only the most highly valued foul is counted.
Not hitting the ball "on" first is the most common foul. Players can make life difficult for an opponent by making sure that they cannot hit a ball "on" directly. This is called "laying a snooker" or putting the other player "in a snooker".
Since players receive points for fouls by their opponents, snookering your opponent a number of times in a row is a possible way of winning a frame when potting all the balls on the table would be insufficient for you to win.
If a player commits a foul, and his opponent considers that the position left is unattractive, he may request that the offender play again from that position.
If a foul has been committed by not hitting a ball "on" first, or at all, and the referee judges that the player has not made the best possible effort to hit a ball "on", and neither of the players are in need of snookers to win the frame, then "foul, and a miss" is called. In this instance the other player may request that all balls on the table are returned to their position before the foul, and the opponent play the shot again. (In top class play, this will usually require only the cue ball and a couple of other balls to be moved.) It should be noted that this rule is often applied less stringently, if at all, in amateur matches.
When a player leaves an opponent unable to hit both lateral extremities of at least one ball "on" after a foul, the opponent will receive a free ball. This means any colour can be nominated and played as the ball "on". The number of points for potting the free ball is not the worth of the nominated ball but of the original ball "on". For example, if the ball "on" is a red, and the free ball is a pink, the player will receive one point for potting the pink. After potting the free ball as a red, a player can nominate and pot a colour as usual.
The end of a frame
A frame normally ends in one of five ways:
A concession, when one player gives up due to being too far behind to have a realistic chance of winning the frame (usually when at the snookers-required stage).
When the pink is potted and the difference between the players' scores is more than seven points. The frame is over and, while the striker may pot the black (for a clearance break, for example), no further shots are necessary.
The black is potted AND the seven points scored puts one player ahead.
A foul on the black AND the seven-point penalty puts one player ahead. It is sometimes wrongly assumed that play continues after a foul on the black if there are then less than seven points in the scores. This is not the case: the player who has made such a foul has lost the frame.
If, however, the black is fouled or potted and the resulting seven points bring the scores level, the black is respotted. Play continues from in-hand, with the players tossing a coin for the choice of playing first or making the opponent play first. Potting or fouling a respotted black ends the frame.
There are two much rarer ways to end a frame:
A player will forfeit a frame due to a failure to hit a ball "on" three times in a row (provided the player was not snookered, in which case the player has as many opportunities as is required).
Should a player refuse to take his turn at any stage, the referee would have the right to declare the frame over.