Dropkick Murphys Singer Beats the CRAP Out of Nazi Skinhead On Stage

**WARNING EXPLICIT LANGUAGE**

ATTENTION NAZIS: stay the hell away from Dropkick Murphys concerts ... or they will kick your ass on stage.

This story is crazy ... the Murphs were playing a show at Terminal 5 in NYC last week when they invited the crowd on stage for a couple songs ... including AC/DC's "TNT" ... and some skinhead dumbass started doing the Nazi salute in time to the music.

Singer Ken Casey caught the sieg heiling out of the corner of his eye ... and stormed across the stage (look on the left at start of the video), chokeslamming the Nazi toolbag and then swinging his bass at him ... at which point chaos erupted.

Ken emerged from the melee roughly 30 seconds later, and shouted into the microphone, "Nazis are NOT F***ING WELCOME at a Dropkick Murphys show."