reacting to a thief?

[JaBlue]

On Caltrain yesterday a big black construction worker tried to jack my $4,000 sick-ass mountain bike. He went towards the front of the car with another construction worker he was sitting next to. That guy's bike was under mine (put a yellow tag on it, [censored]). Black dude helps him take off my bike so other guy can grab his, then tries to walk off the train. I'm right behind this [censored], calmly grab my bike and say "dude." Guy just keeps walking off the train and away. I'm taking the train to the next stop.

I was tired and stressed from earlier, and looking forward to the bike ride later and without thinking much about it, just let him go.

What do you do in this situation? What if it was your stop too?

Black dude is big and strong and can whoop you and five other people's ass.