The cops were duly called by the community security guard to deal with a crowd of rowdy tresspassers.
The tresspassers should have been picked up bodily by a force of residents, dragged to the gates and tossed out.
The story mentions absolutely nothing about any "security guard".
For that matter it also mentions absolutely nothing about "trespassing".
Well, the story is available, and from what I've been able to put together, it went something like this.
A kid in that complex had a pool party to celebrate the end of school. He invited a bunch of friends and gave them guest passes. Those kids invited more kids, as kids will do - and many people without passes ended up sneaking in.
Other residents of the complex, seeing far too many black people in the pool for their comfort, called the complex security and then the police - also, some racist lady got in some of the kids faces and started a fight with them.
Then the cops came, then the video started recording.
A lot of posters here seem to have jumped to the conclusion that the girl in the video was one of those dastardly "trespassers", for unclear reasons.
That's exactly what I've inferred from available info.
I word-searched the page for "security" and "trespassing"; neither showed up.
Being present within the gates of that private pool without a guest pass could be considered trespassing, and one of the calls to the police came from the complex security guard.
You must have a link we haven't seen.
The first part is an assumption, but a pretty easy one to make. The second I believe I saw in a link you provided - the Buzzfeed one.