behind the eight-ball

First use appears c. 1923 in the Buffalo Evening Times. 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 from eight-ball pool, where one cannot contact the eight ball on a shot before it is the legal ball, frustrating shots, or more generally, from the fact that the 8 ball is considered harder to aim at because of its color.