After repeated watching of the video, it appears most of the beating of Villa and Westberry was done by an LAPD sergeant.
Villa and Westberry were standing on the street videoing. An officer on bicycle comes behind them, picks up his bike, slams it into them, pushing them into the Sgt., who pushes back. They get pushed again, and the Sgt. hits them once while standing, then more four times after they are lying on the sidewalk. The final hit (photo 1) was after a pause of a few seconds, and another officer then backs him off (photo2).