Looks to me like skateboardbitch was swinging that board like a blade, at the base of the kid's skull. Very easily a fatal blow.
'Lefty' was pointing a pistol at the kid's face.
Littleangryman apparently threw a brick in a bag, just before getting brained. I didn't see good vid on that one though.
I wasn't there, but it seems like a lot of defensive shooting to me.
Skateboards are the antifa weapon of choice because they can carry them without overly calling attention to themselves. The carriage on each end of them adds quite a bit of mass and it's easy to see how they can cause a lot of damage when using them as an edged bludgeon.
The bicycle locks with the large loop are another weapon favored by antifa.
