Cue sports playing nine-ball. Snooker balls are smaller than American-style pool balls with a diameter of 52.5 mm ( in), and come in sets of 22 (15 reds, 6 "", and a cue ball). English billiard balls are the same size as snooker balls and come in sets of three balls (two cue balls and a red, an object ball). Other games, such as bumper pool, have custom ball sets. Billiard balls have been made from many different materials since the start of the game, including clay, bakelite, celluloid, crystallite, ivory, plastic, steel and wood. The dominant material from 1627 until the
Rules of snooker is a touching ball; the striker must therefore play away from all of them. The striker scores no points for balls potted as the result of a foul. Depending on the situation, these balls will either remain off the table; be returned to their original spots; or be replaced in the positions they occupied before the foul shot, along with any other balls that were moved during the shot. For details on such situations, see Fouls below. Each frame of snooker generally consists of two phases. The first phase lasts as long as any red balls remain on the table.