Green’s Dictionary of Slang

(US prison) of a prisoner, to fraternize with the prison authorities; thus leg-hanger, one who pursues such acquaintances.

1992

Bentley & Corbett Prison Sl. 32: Hangin’on the Leg also Leg Hanger To fraternize eagerly with prison staff. Hangin’ on the leg, in prison, is a disgusting form of fraternization as it is a general rule of inmates not to associate with prison guards or staff members. Prison staff have no respect for leg hangers.