Under an old Illinois law, not only can persons who lose at unlawful gambling sue the winners to claw back their losses, but if they fail to act, literally any other person can sue demanding that money. Citing this law, two women sued online-poker operators seeking to recover gambling losses of men who happened to be their sons (but could as easily under the law have been strangers). A Seventh Circuit panel, Judge Posner writing, has now upheld a lower court’s dismissal of the case (an intended class action) on the grounds that the Illinois law by its terms allows suit only against the other gamblers who won the poker games in question, not the house that collected a fee for presiding. [Courthouse News, Rakebrain; opinion in Sonnenberg v. Amaya Group Holdings via John Ross, Institute for Justice “Short Circuit”]
While on the subject of Judge Posner, Harvard Magazine has a Lincoln Caplan interview with him that is worth a read.