九号球是撞球运动的其中一种玩法，起源于1920年代的美国。在任何社交场合，不论人数多寡都可玩九号球（大多是一对一），只要在游戏开始前定好规则即可；在联盟或巡回赛的场合里，选手的人数和规则是由比赛赞助者订定。以往，不论是职业级或是业余级，九号球常被当作「赌博性的游戏」，但现今的大型巡回赛里，九号球的光环未失。

近年来，九号球成为美国境内巡回锦标赛的其中运动之一，主要是因为比赛速度较快，符合电视转播的时间限制，而持续吸引观众的参与。多年来，运动频道ESPN是主要促进九号球运动的推手，也是巡回锦标赛的赞助者。

Nine-ball (sometimes written 9-ball) is a contemporary form of pool (pocket billiards), with historical beginnings rooted in the United States and traceable to the 1920s. The game may be played in social and recreational settings by any number of players (generally one-on-one) and subject to whatever rules are agreed upon beforehand, or in league and tournament settings in which the number of players and the rules are set by the sponsors. During much of its history, nine-ball has been known as a "money game" in both professional and recreational settings, but has since become established as a legitimate alternative to eight ball, straight pool and other major competition games.