The comments seem to be largely in defense of the driver.
Here's what I can make out:
it was a "holiday" or a "celebration" for motorcycles that day. That much is obvious, can't even count how many there are. So, drivers are upset that motorcyclists are all over the road. As Fleck said, horns are honked, fingers given, curses yelled, etc etc. It looks like what sets it off is the riders get pissed, one brake checks the RR, and the driver gives him a love tap (it happens just off screen, but I can't see anyone go flying, so I think the rider stayed upright). Don't know if it was purposeful or not, I've never understood the rationale behind brake-checking a 4 wheeled vehicle that outweighs your 2 wheel vehicle by thousands of pounds. After the brake check, they get pissed off, stop traffic, and from there it's on like donkey kong.
Again, I think all sides acted worse. I think the riders over-reacted a little bit in the beginning, but after seeing comrades get run over, I'd be hard pressed to imagine many on this board wouldn't do the same (if we could go that fast!).
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@adamwfurlong