It's hard to tell on my iPad, but didn't look to me like the guy hit his brakes that hard.(but maybe he did)
Either way, that's when you dial 911. I doubt anyone would have been breaking windows or busting heads at that point. His big mistake was running over several bikes and riders after the initial incident.
this doesn't look like a gang of outlaw bikers to me.
i ask again, what would YOU do if your friend was run over (intentionally) by an SUV and almost (or) killed?
Got the guys license plate number and called 911 to report a hit and run. And ask for medical help for my friend.