 Many billiard-specific and etymological sources point to kelly pool, or an early version of the game called kelly rotation, as the origin of the common idiom, "behind the eight ball".Some publications blithely assume the expression to be eponymously derived from the game of eight ball, but it has been pointed out that the expression came into use before eight ball was popularized, and that the game did not even use an "actual 8 ball" under the version first marketed to the public.The predecessor to the BCA, The National Billiard Association, meanwhile, holds that the expression simply emanates from the fact that the eight ball, being black-colored, is harder to see than other balls, thus resulting in an association with any difficult position.