Abandoned bikes

If you see a guy that you think is trying to steal a bike, do you go up to him and say something? Do you approach a man with chisel and hammer? What about a group of kids kicking in a bike? I dont like to say it, but not being a pure burly bloke i probably wouldn't

my dad confronted a man with a hammer and chisel once, so I like to think I'd have the courage to do the same.

but I am a chip off the old block.