A very, very long time ago, shortly after I left the military, I jumped a purse snatcher in San Francisco. Literally.

The funny thing is I don't remember doing it. I remember my partner and I were on the very busy Castro Street sort of wandering around playing tourist and enjoying ourselves.

I remember hearing a scream and seeing a tall stocky man jerk a purse out of the hands of a very elderly woman. I remember seeing him stride rapidly away from her, in my direction, the crowd clearing for him like the parting of the Red Sea.

A few moments later I found myself on the ground with a police officer bending over me asking if I was okay. "You gotta be more careful," he said. "That guy had a knife. A purse isn't worth your life."

My partner later told me I jumped on the guy's back when he started to pass me, grabbing the purse, at which point a large pocket knife clattered to the ground. I got the purse, but the guy got away. Nobody but me tried to stop him.

I think it all happened so quickly that people just froze. I didn't have time to evaluate risk any more than anyone else did. Jumping the guy was dumb. I could have just followed him at a safer distance while shouting for help and the police.

I had some hand-to-hand fighting training from the Marine Corps reserves before I went active duty Air Force. I also had boxing experience from my adolescence. But I didn't use any of that training.

I just jumped without even deciding to.

There had to be a hundred people within 100 ft, and I was the only person who acted, and even I didn't act on purpose.

The whole course of events lasted perhaps 45 seconds before the guy was gone.

That's not enough time for most people to process what's happening, let alone do something to help.

So yeah, I'd agree that inspecting help from strangers on the street is pretty unrealistic.