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.
2021		‘Aidan Truhen’ Seven Demons 311: So someone will make nasty and get smacked down.

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’.