Video taken by witnesses showed a man with a snare drum sneaking up on a female officer and striking her in the back of the head. She suffered a concussion with the force of the blow, which put a dent in her helmet.
The Los Angeles Police Department said Brian Mendoza was arrested Wednesday in connection with that attack. He was being held without bail.
Meantime, police are still looking for a group that attacked officers with a wooden pallet. The suspects dropped the pallet and escaped into the crowd.
Anyone with information was asked to call police at (877) LAPD-24-7.