stylistic:style_transfer, structural:reformatting
Objective

A player wins a frame by scoring more points than their opponent. At the start of a frame, the object balls are positioned on the table as shown in illustration A. Starting with the cue ball in the "D", the first player executes a break-off shot by striking the cue ball with the tip of their cue, aiming to hit any of the red balls in the triangular pack. The players then take alternating turns at playing shots, with the aim of potting a red ball into a pocket and thereby scoring one point. Failure to make contact with a red ball constitutes a foul, which results in penalty points being awarded to the opponent. At the end of each shot, the cue ball remains in the position where it has come to rest, unless it has entered a pocket (from where it is returned to the "D"), ready for the next shot. If the cue ball finishes in contact with an object ball, a touching ball is called; the player must then play away from that ball without moving it, otherwise the player will concede penalty points.

When a red ball has entered a pocket, the striker must then choose a coloured ball (or "colour") and attempt to pot it. If successful, the value of the potted colour is added to the player's score, and the colour is returned to its designated spot on the table. The player must then pot another red ball followed by another colour. The process of alternately potting reds and colours continues until the striker fails to pot the desired object ball or commits a foul—at which point the opponent comes to the table to start the next turn—or when there are no red balls remaining in play. Points accumulated by potting successive object balls are called a " break " (see Scoring below). At the start of each player's turn, the objective is to first pot a red ball, unless all reds are off the table or the player has been awarded a free ball, which allows them to nominate another object ball in place of a red. The cue ball can contact an object ball directly or it may be made to bounce off one or more cushions before hitting the required object ball.

The game continues until all fifteen red balls have been potted and only the six colours and the cue ball are left on the table. The colours must next be potted in the ascending order of their values, from lowest to highest, i.e. yellow first (worth two points), then green (three points), brown (four points), blue (five points), pink (six points), and finally black (seven points); at this stage of the game, each colour remains in the pocket after being potted. When the final ball is potted, the player who has accumulated the most points wins the frame. If there are not enough points remaining on the table for a player to potentially win the frame, that player may offer to concede the frame while at the table (but not while their opponent is still at the table); a frame concession is a common occurrence in professional snooker. However, players will often play on even when there are not enough points available for them to win, in the hope of laying one or more " snookers " to force their opponent into playing foul shots. Snookers are shots designed to make it difficult for the opponent to play a legal shot on their next turn, such as leaving another ball between the cue ball and the object ball.

If the scores are equal when all object balls have been potted, the black is used as a tiebreaker in a situation called a " re-spotted black ". The black ball is returned to its designated spot and the cue ball is played in-hand, meaning that it may be placed anywhere on or within the lines of the "D" to start the tiebreak. The player to take the first strike in the tiebreak is chosen at random, and the game continues until one of the players either wins the frame by potting the black ball or loses the frame by committing a foul.

Professional and competitive amateur matches are officiated by a referee who is charged with ensuring the proper conduct of players and making decisions "in the interests of fair play". The responsibilities of the referee include announcing the points scored during a break, determining when a foul has been committed and awarding penalty points and free balls accordingly, replacing colours onto their designated spots after being potted, restoring the balls to their previous positions after the " miss " rule has been invoked (see Scoring below), and cleaning the cue ball or any object ball upon request by the striker. Another duty of the referee is to recognise and declare a stalemate when neither player is able to make any progress in the frame. If both players agree, the balls are returned to their starting positions (known as a " re-rack ") and the frame is restarted, with the same player taking the break-off shot as in the abandoned frame. Professional players usually play the game in a sporting manner, declaring fouls they have committed that the referee has not noticed, acknowledging good shots from their opponent, and holding up a hand to apologise for a fortunate shot (known as a " fluke ").