Penguin Book of historical slang
Black-leg, v. (Tailors') to boycott a fellow-tailor: ca 1870-1910. 2. v.i., or as black-leg it, to return to work before a strike has been settled: from ca 1885; coll.
Black-legged, adj. Swindling: c. of ca 1790-1850. (Anon, ballad, The Rolling Blossom, ca 1800.)
Black-leggery. Swindling: Maginn, 1832; coll; S.E. by 1850, but never very common.
Jim Carroll