Holy crap! I can’t believe that Kirk Hammett kicked a beach ball at Joey Belladonna and knocked him off the stage. That seems so…oh wait…different incident.

The Metallica guitarist joined Anthrax onstage during their show at the Warfield Theatre in San Francisco last night (October 23). Hammett sang guest vocals on “I Am The Law” and then played an abridged cover of Metallica’s “Whiplash” with the band (while Scott Ian played air guitar).

While Hammett joined the band onstage, it turns out that backstage was packed with some famous faces as well. Ian posted the picture above of him and drummer Charlie Benante hanging out backstage with Hammett, Slayer guitarist Kerry King, Exodus guitarist Gary Holt, and Death Angel singer Mark Osegueda. Too bad the last three didn’t join Hammett onstage for a mini-Big 4 jam (though Osegueda did jump up onstage following the “Whiplash” cover to start an “ANTHRAX” chant).

Fan filmed clips of Hammett joining Anthrax onstage can be seen after the jump.