What would you do if you're a random guy--in this case, an unarmed security guard--and an entourage of around ten big-ass black guys looking like a football team were pummelling somebody? You don't get involved, unless you're willing to get pummelled alongside the unlucky guy. If a cop sees a gangfight, he doesn't just jump in the middle with his badge and yells "stop," he calls for backup first.