Sometimes interchangeable with scratch, though the latter is often used only to refer to the foul of pocketing the cue ball.
A violation of a particular game's rules for which a set penalty is imposed. In many pool games the penalty for a foul is ball-in-hand anywhere on the table for the opponent. In some games such as straight pool, a foul results in a loss of one or more points. In one-pocket, in which a set number of balls must be made in a specific pocket, upon a foul the player must return a ball to the table. In some games, three successive fouls in a row is a loss of game. In straight pool, a third successive foul results in a loss of 16 points (15 plus one for the foul).
Possible foul situations (non-exhaustive):
• The player shoots the cue ball first into a ball that is not an object ball;
• The player shoots and after contacting an object ball, no ball is pocketed and neither the cue ball nor a numbered ball contacts a cushion (excepting push out rules);
• The player pockets the cue ball (see scratch);
• The player does not have at least one foot on the floor at the moment of shooting;
• The player shoots the cue ball before all other balls have come to a complete stop;
• The player hits the cue ball more than once during a shot (a double hit);
• The player touches the cue ball with something other than the tip of the cue;
• The player touches any ball other than the cue ball;
• The player causes a ball to leave the table's playing surface without it returning (e.g., jumping a ball off the table);
• The player marks the table in any manner to aid in aiming;
• The player who has ball-in-hand, touches an object ball with the cue ball while attempting to place the cue ball on the table;
• The player shoots in such a manner that his cue tip stays in contact with the cue ball for more than the momentary time commensurate with a stroked shot (a push shot).