They're just wanna be cops. Rent a cops. I don't know about laws over in the US but here in England you're allowed to film anyone in public, meaning that guard in the first one would have made the first attack. They think they have shit loads of power because they wear a badge. Why don't they just ask them politely to move on instead of getting physical to start with? That's why people think Skaters are "punks" because they stand up for themselves.
I hate cops and security guards are people who can't be a cop. They only become a cop or guard because they aren't smart enough to gain any true power so they use this method of gaining power and abuse it. They act like douchebags. I lol'd at the fat guard crashing his go-cart.