DROPKICK MURPHYS singer and bassist KEN CASEY attacked a skinhead who did a NAZI SALUTE onstage during their concert in Manhattan last week.  Naturally, this ignited some chaos . . . but after the situation calmed down, Casey took the mic and said, quote, "Nazis are NOT [EFFING] WELCOME at a Dropkick Murphys show."

WARNING: NSFW...unless you watch it on mute to filter the profanity.

(Skip to 1:15.  At 1:30, Ken swings into action.)