How the game is played
The black ball is placed on the lowest spot, roughly 32 cm from the top cushion. The blue spot sits exactly in the middle of the table. The spot the pink ball goes on lies between the blue spot and the top cushion.
The fifteen reds are packed tightly into a triangle using a rack, and placed as close under the pink as possible without touching it. In practice the referee usually sets the reds first and puts the pink on its spot last. Across the top of the table runs a straight line (the baulk line) with a semicircle on it (the D). Seen from the bottom of the table, the yellow ball sits on the left-hand junction of the line and the semicircle, the green on the right, and the brown in the middle.
The white ball (the cue ball) may be placed anywhere inside the semicircle by the player breaking off. With that cue ball, the balls have to be potted in a set order. A player must always pot a red first. If he does, he then plays a colour, which he names before the shot (this is called "calling"). In practice this only happens when it is not immediately obvious which ball he is playing. If the colour is potted too, it is returned to its own spot and the player must play a red again. Reds stay down once potted, so they are not returned to the table, not even if they were potted illegally or jumped off the table. For every ball potted the player is credited with the value of that ball (see below) on the scoreboard.
The number of points a player scores in succession — that is, without missing a ball — is called a break. When a break ends, either by failing to pot or by committing a foul, it is the opponent's turn, and he too has to start with a red. This continues until the last red has been potted. The player may then choose a colour one final time. If he pots it, the ball is returned and he continues; if not, it is the opponent's turn. All the colours are now cleared in order of their value.
The order is (value in brackets): yellow (2) – green (3) – brown (4) – blue (5) – pink (6) – black (7).
Whoever has the most points after the last ball is potted wins the frame (a single game). The opponent may also concede earlier if the gap has grown too large and he can hardly force any further mistakes. A frame ends when all the balls have been potted; or when only the black is left, the gap is more than seven points and the player due to play chooses not to continue; or when a foul is committed with only the black left on the table; or when the referee awards the frame to someone on the basis of another rule.
A match consists of a set number of frames. It ends as soon as one of the players has won the majority of them. In a match over 19 frames (best of 19), that means the match ends once one player has won 10 frames. Big matches are often spread over several sessions of, say, 8 frames.
Points of detail
The ball being played (a red, or a colour that has been called) is known as the ball-on. The player must strike this ball-on first with the cue ball, or penalty points follow. If the ball-on cannot be struck directly, usually because another ball is in the way, the player is said to be snookered.
It also happens occasionally that, with the cue ball resting on the lip of a pocket, the edge of the cushion prevents it from striking the ball-on in a straight line. In that case the cue ball is said to be angled.
Potting two or even more reds in a single shot is allowed — the player scores one extra point for each additional red. If the spot of a colour is occupied, the ball goes on the highest-value spot that is free. If every spot is occupied, the ball must be placed as close as possible to its own spot, on the centre line of the table, as close to the top cushion as possible. If several colours have to be returned, the highest-value ball takes priority.
If a foul is committed while only the black remains on the table, the frame is over. The opponent receives seven penalty points, and the final score decides who wins the frame.
If the scores are level at the end of a frame, the black is re-spotted (the re-spotted black) and the cue ball is placed anywhere in the D. A coin toss decides who is to play; that player may choose whether to play himself or make his opponent play. Whoever pots the black first wins the frame. On a foul — potting the cue ball or missing the black — the opponent wins.
Fouls
- Potting the cue ball (into a pocket or even off the table), or making it "jump" over a ball when that ball is causing a snooker (that is, when it is in the way). A potted cue ball is placed anywhere in the D by the opponent, who may then play towards any side of the table.
- Striking no ball, or striking the wrong ball first.
- Potting the wrong ball.
- Touching a ball other than the cue ball, or touching the cue ball with anything other than the tip of the cue.
- Tip, cue ball and ball-on being in contact at the same time. In other words, no push shot when the cue ball and the ball-on lie very close together. If they are touching, a touching ball is called and the player must play away from that ball. In doing so he must not strike any ball that is not on.
- Not having at least one foot on the floor while playing a shot.
- Playing while not all the balls are on the table (for instance when a colour has not yet been returned), or while the balls have not all come to rest.
Fouls are punished with penalty points; these are not deducted from the offender's score but awarded to his opponent. The number of penalty points is always the value of the highest-value ball involved in the foul (the ball-on, a ball wrongly potted or struck first, and so on), but never fewer than 4 points.
Playing at a red and hitting nothing therefore costs 4 penalty points; hitting the black instead of another ball costs 7. If several fouls are committed in one shot, the one carrying the most penalty points counts.
A foul also cancels any points already made on that shot. If a red is potted correctly but the cue ball drops in as well, the player scores nothing and only the penalty points are awarded. Points made on earlier shots in the break are of course not lost. If a player has already made 10 points in his break and fouls on the next shot, he keeps the 10 points and his opponent receives the penalty points for the foul.
After a foul it is the opponent's turn, but he may ask the offender to play again. In that case the offender has to play "again", though the balls are not returned to where they lay before the foul. In practice this is only done when the foul has left the opponent without a decent opportunity. Any free ball (see below) is lost when the shot is handed back.
Free ball
If, after a foul, the balls come to rest in such a way that the term snooker applies — the ball-on cannot be struck directly on either side because one or more other balls lie in between — a free ball is awarded. The opponent may then "nominate" any other ball as the ball-on. That ball then also carries the value of the ball-on, whatever its normal value. If the nominated ball is a colour, it is returned to the table after being potted.
If the free ball is awarded in place of a red (so the player would normally have had to play a red),
then once he has potted the free ball he may play a colour, even if the free ball he chose was itself a colour.