Green’s Dictionary of Slang

1. to hit hard, esp. to hit in the face.

1925		D. Hammett ‘Corkscrew’ Story Omnibus (1966) 217: I got a great mind to smack you down!
1939		J.T. Farrell Tommy Gallagher’s Crusade 74: They ain’t worth smacking down, these bums.
1956		‘Ed Lacy’ Men from the Boys (1967) 13: I asked you in a nice way, but you hardheads got to get smacked down.
1967		P. Thomas Down These Mean Streets (1970) 16: Nobody really digs a kid. But a man—cool. Nobody can tell you what to do—and nobody better. You’d smack him down like Whiplash does in the cowboy flick.

2. to tell off, to reprimand, to put in one’s place.

1937		P. Cheyney Dames Don’t Care (1960) 37: The little guy who has just been smacked down gets up an’ walks outa the room.
1960, 1975		Wentworth & Flexner DAS.
2008		in J. Miller Getting Played 101: ‘Smack her down then, tell her to shut up’.