behind the 8 ball: in a disadvantageous or precarious position. Originally derived, in the early 20th century, from a billiards game called pill pool (aka Kelly pool or pea pool), the 8 ball in that game occupies a uniquely dangerous position: if your ball is directly behind the 8 ball, you are blocked. The position is not merely difficult: it is practically impossible. You cannot win by skill alone. The idiom became popularly applied to serious trouble in the 1930s, when the economic Great Depression raged.