Definition: Any foul or infraction of the game rules. Most games require that balls pocketed during an illegal stroke or in an illegal manner (such as knocked into the pocket by the brush of a player’s arm before the stroke is made) be returned to the playing surface.
Examples:
It is illegal in all pool games to make the cue ball jump off the felt by scooping the ball into the air using the cuestick rather than striking down at the ball with the cue tip.
