Green’s Dictionary of Slang

(US black) to malign, to criticize, to gossip about someone; thus sniping n.

1932		J. Dixon Free To Love 210: ‘If you’re going to snipe, like Julia—’ the babyish face puckered again. ‘I’m not sniping. [...] I want to help you.’.
1967–8		Baker et al. CUSS 200: Snipe Make uncomplimentary remarks about someone.
1978		R. Caron Go-Boy! 268: The three uniformed goons [...] were their usual petty, sniping selves.
1980		E. Folb Runnin’ Down Some Lines 198: There were terms related to gossip and those who gossiped: [...] snipe, deal/do dirt (gossip, talk badly about someone).
1992		D. Jarman letter 4 Apr. Smiling in Slow Motion (2000) 112: I hope this continual sniping doesn’t undermine what is left of my health.
2000		Guardian G2 3 Feb. 12: Scott Hicks won seven Oscar nominations [...] with his film Shine. But that didn’t stop the sniping at his latest effort.