 It is often assumed that the expression derives from the inability to use the 8 ball in a combination in the game of eight-ball – if the cue ball is directly behind the 8 ball a player has no direct shot.However the expression derives instead from kelly pool, as eight-ball was a less common, still developing game at the time the phrase arose.It refers to players assigned balls numerically higher than 8 – that is, balls that are "behind the 8 ball in order" – who have less chance of winning, as the odds that other players have lower winning numbers increases for players with higher numbers.