behind the eight-ball

Thought to derive from the game of Kelly pool, in which players assigned balls numerically higher than 8—that is, balls that are behind the 8 ball in order—have little possibility of winning, or more generally, from the fact that the 8 ball is considered harder to aim out because of its color. Some sources have pointed to its origin as the game of eight ball, but eight ball was popularized after the expression was already in use (by at least 1919), and at the time of popularization, called then B.B.C. Co. Pool, was marketed with a ball set that did not not include an actual 8-ball, but rather seven balls of one color, seven of another, and an unnumbered black ball.