[svandamme]

That ain't smart, running after an unknown perp like that in the dark.
For all you know his buddy who drove him there is waiting for you and they stick a knife in ya.

over a dirt bike?? worth what? 1500 bucks? (i don't know prices for those down there).
Is your life only worth that much?

also, what are self defense laws in NZ like???
If in a scuffle he trips and falls badly with his skull on the curb.. and ends up veggie state..
Will his family come after you in court?
You ran after him, so it's no longer self defense is it?