It's as easy as saying, "fuck of, kook" and leaving the minute Jensen throws the board into the street. I think Dela is largely responsible for it getting violent...
We all know there are systemic issues with cops and other figures of authority abusing their power. From your description of the footage, Jensen seemed eager to prove something and was aggressive, like a lot of cops and security are. But Dela immediately shoved him when the board was tossed, quickly matching that energy and kicking off the power struggle that never should have occurred. Instead of yelling at his friend to leave it alone, Jesse does act to further escalate the situation by kicking the walkie talkie. The guard should have had more self control and not charged at a group of young men holding skateboards, and I'm willing to bet he wasn't trained to try to beat up on skateboarders. However, if they had the sense to leave the spot, none of it would have happened.
We need to remember that these guys weren't just harassed for walking down the street. They were engaged in clearly prohibited activity, and no matter how good the clip is going to be, when it's time to stop it's time to stop. The confrontation is not worth it, even if it never moves past shouting. Skateboarding is not some terrible activity that needs to be squashed with hostility like it so often is, but until shit changes just keep it moving when the time comes.