NBA star J.R. Smith beat the living daylights out of a man who allegedly smashed his car window during the wild protests in L.A. ... and TMZ Sports has the video.
You can see ... the 6'6", 225-pounder unleashed a barrage of violent kicks on the man -- landing several times in the head.
When the guy finally stands up on his feet, Smith delivered a final punishing overhand right to the guy's dome.
Finally, some of J.R.'s friends step in and the other guy scurries off in a hurry.