Six-ball is essentially identical to nine-ball but with three fewer balls, and racked in a three-row triangle , with the 6 ball (or more often the 15 ball; see below ) as the money ball , placed in the center of the back row. According to Rudolph "Minnesota Fats" Wanderone, the game arose in early 20th century billiard halls that charged by the rack instead of by the hour, as nine-ball players had already paid for the 1015 balls and did not want to waste them. This explanation of the game 's origin may be particularly plausible because six-ball remains popular today as a diversion or practice round among nine-ball -playing bar pool players, using coin-operated tables that deliver a full set of fifteen balls.