Green’s Dictionary of Slang

1. a blow, a punch; a bullet wound.

1798		W. Pitt the Yngr in Lord Rosebery Life (1891) 208: The bill is to be read a second time tomorrow, and, in spite of many Plugs from Sir W. Pulteney, will certainly pass [OED].
1848		‘Ned Buntline’ Mysteries and Miseries of N.Y. V 65: A plug muss is rich.
1867		E.B. Christy Box And Cox in Darkey Drama 6 9: Now don’t kick up a plug muss, gemmen.
1890		Sporting Times 22 Feb. 2/3: The obvious consequence is that you don’t give a man a plug in the eye in a hurry.
1897		W.T. Goodge ‘Great Aus. Slanguage’ in Baker Aus. Lang. (1945) 117: If he hits a man in fighting / That is what he calls a plug.
1906		A. Adams ‘Rangering’ in Cattle Brands 🌐 Just then I got a plug in the shoulder, and things got dizzy and dark.
1906		Marvel 6 Oct. 309: If you get a plug on the nose it will.

2. (US) a prizefighter.

1904		O. Kildare Good of the Wicked 17: ‘Plug’ Duffy, a dimly glittering star of the fistic firmament.
1906		S. Ford Shorty McCabe 149: He’s won more bouts by scarin’ his man stiff than any plug in the business.