XXXTentacion Knocked Out Onstage, One Person Stabbed

XXXTentacion got sucker punched onstage and knocked out cold during his show in San Diego … which turned into an all-out brawl that left one person stabbed.

The video of the attack is insane — XXX was up on the mic performing Wednesday night when the attacker socked him out of nowhere. Security scrambled and beat the piss out of the unidentified puncher.

Law enforcement sources tell us the stabbing happened backstage after the initial punch.