From what I can tell, the officer gets out of his car with his gun holstered. He's trying to access the situation and from around a vehicle, a lady comes crashing into the ground in front of him and a girl with a knife is pursuing her. The officer then draws his weapon. Some guy comes over and kicks the girl that fell to the ground and the girl with the knife then charges another female wearing pink who's pinned up against a car. She leans away from the girl with the knife and puts her leg up as a defense mechanism. The girl pulls her arm with the knife back likes shes winding up for a hard stab and the officer shoots her. I don't know how much the officer knew about the situation or if he just pulled up when the footage starts, but it seemed like he was trying to save the lady in pink's life in that moment.