Four people are facing gang assault charges following an assault Wednesday afternoon. Rochester police say Xavier Lopez, 17, Brandon Purdie, 19 both of Rochester, and two 16-year-olds are charged with first degree gang assault. A citizen who saw the live stream called 911 and police found the wounded man. The teenagers matching the suspect descriptions were spotted nearby and were arrested after simultaneous foot chases. Video shows one of the teens walk up and punch the victim in the back of the head, knocking him to the ground outside the Transit Center. Police call it a horrific, unprovoked attack. Police say the victim suffered injuries to his head including "multiple nasal and facial fractures."