Green’s Dictionary of Slang

1. (US campus) unfair.

1900

E.H. Babbitt ‘College Words and Phrases’ in DN II:i 60: skin, adj. 1. Unfair. 2. Mean.

2. (US) crooked, corrupt, e.,g. of a casino.

1870		Eve. Teleg. (Phila., PA) 1 Feb. 5/2: The principle skin-faro bank is located at no., 903 Chestnut Street [...] It would take up too much space to go into the details of the means employed, the perseverance, ingenuity, and devices used to entrap victims in these gambling hells.
1882		A. Trumble Crooked Life in Nat. Police Gaz. (NY) 8 July 6/2: A confidence operator in Chicago [...] picked up a man [...] one afternoon and took him to a ‘skin’ gambling house where, as he said, they dealt a perfectly fair game .
1913		Day Book (Chicago) 11 Nov. 3/1: Hearst isn’t the kind of man who would get acquainted with a stranger and steer him up against a brace poker game, the big mitt, or a skin faro layout, and get part of the money for landing the sucker.