I'd want to know who those guys on the passenger side are.
Who else is around? Does a, "hey what up", send the bad guy running? Sometimes it does? I'd go that far. How about, "the cops are on the way"? How about a 911 call? Let's say I know the guys on the passenger side aren't involved, they aren't the bad guy's friends, or I'm pretty sure they aren't. I might think about getting involved, based on that video. I don't want to see an old guy get beaten to death, but I'm still not up to killing the bad guy, if that's the question. I'd be worried if I thought he had friends. A gun would still not be on my list of tools to employ.
OK, here's a real life senario I've been waiting to bring up: You see one drunk threatening another guy with a knife. It's looking bad. The other guys got his hands up and is backing away. A lot of people are standing around. People are yelling, "knock it off", or "calm down". The guy with the knife has his back to you. You are worried the other guy is going to get hurt or killed. Are you justified in shooting the guy with the knife? If I told you I ended that situation with an arm bar and and wrist lock, and based on the fact that worked, I don't think a person would be justified in using deadly force, what would you say?