A man at a protest against police brutality in Berkeley, California, was knocked out with a hammer on Sunday night after he tried to stop looters.

Disturbing footage of the incident was captured on camera by Berkeleyside reporter Emilie Raguso.

The brief video shows a man in a bicycle helmet pushing protesters wearing black hoodies outside a Radio Shack on Shattuck Avenue in Berkeley. One of the protesters then smashes a hammer into the man’s head, and he drops to the ground.

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“Tensions rose after the man was assaulted,” Berkeleyside reported. “There was a series of aggressive interactions between protesters who wanted to keep the peace and stop those who were breaking windows at Radio Shack and those who were encouraging the vandalism. Several of the aggressive protesters who saw people taking photos and videos became very menacing and ordered them to stop recording.”

The injured protester was taken to the hospital with non-life threatening injuries, and police are investigating the incident.

Watch the video below: