Green’s Dictionary of Slang

(US black/gang) a member of the Black Gangsters or New Breed.

1996		Jrnl Gang Research Winter 64: The BG’s are an all-black renegade gang that defies classification along the folks/peoples gang alliance system.
2021		S.A. Crosby Razorblade Tears 17: I did a nickel at Red Onion. [...] Met a few BG boys out there.