Green’s Dictionary of Slang

(US) a street gang that has regular fights with opponents.

1959		H. Salisbury Shook-Up Generation (1961) 17: The Cobras are an active ‘bopping’ or street-fighting club. [Ibid.] 22: Heart as defined by the bopping clubs is not the exact equivalent of courage.
2004		at www.palmdigitalmedia.com 🌐 (ref. to mid-1950s) In the mid-fifties, Harlan Ellison [...] took a phony name, moved into Brooklyn’s dangerous Red Hook section and managed to con his way into a ‘bopping club.’.