Not enough information to say. We don't know what happened before the video started rolling. In many states, one of the conditions of being able to use force (of any kind) in self-defense is that you don't provoke or start the incident.
If the guy is walking down the street minding his own business and the video shows all the relevant parts, then the only issue is whether a reasonable person would feel an immediate threat of death or serious injury by their actions and at what point in the video would that occur.
However, if say, before the video started, the victim yelled "Hey you goat-humping, syphillitic morons, watch where you are going!" Well, then we have a question whether that provoked the fight and how hard did the guy try to retreat/leave the fight?
As a rule of thumb, if you draw on an unarmed man (or group of men) and start shooting, expect to go to jail and need a lawyer.* If the circumstances look bad enough that this is the least of your worries, then do what you gotta do.
*For a good example of this, see
Mark Abshire who was attacked on his own lawn by six drunk men, in a state with good gun laws and a "Stand Your Ground" law. Mr. Abshire attempted to use non-lethal force and waited until he was down on the ground with his teeth cracked and one guy on top of him and another guy kicking him to pull his pistol. Despite that, he lost his job, house, and spent two years in the court system.