Ignore? No.
Become directly involved with strangers?
Like clearing mines by tap dancing.
911 isthere for a reason.
Being an ex cop, I'm sure he knows what he is doing.
Those that don't have the experience need to learn and it has been said here many times, think first.
If a woman, child, or elderly person is involved I would cautiously intervene. But the truth of matter is that you must act quickly and you must think on the run. No matter how much you think and evaluate, the situation can always turn south.
It's a moral decision. Walk away and hear the screams for the rest of your life, or do something about it. And the minute you decide to do something about it, you're taking a chance.