Green’s Dictionary of Slang

(US black) to fight, to beat up; to defeat severely.

1985		T.R. Houser Central Sl. 10: beat down [...] ‘The boys rushed him and jus beat down the dude.’.
1990		M. McAlary Crack War (1991) 168: If they’re gonna beat somebody down, or they’re gonna kidnap someobeody [...] I can hear.
2000		P. Beatty Tuff 14: Remember the cat-ass punk you beat down last week.
2001		(con. 1990s) in J. Miller One of the Guys 108: ‘[He] beat her up real bad [...] just beat her down, you know, crushed her’.
2010		Codella and Bennett Alphaville (2011) 45: [He] made his kid rat on the guys whop beat Bruno down.
2018		‘Aidan Truhen’ Price You Pay 55: I got beat down for no good reason.