You could always ring someone at the INZ branch you will be dealing with if you're really worried about it. As you had a conditional discharge and nothing more serious, I would really hope that INZ would have more sense than to take you to task about it, especially as it was a one-of offence. The worst scenario would be that you have to apply for a waiver, but I suspect it wouldn't even come to that. How many people in their drunken youth have taken a pop at someone? Not that I'm saying you were drunk, of course
, but you get my drift. NZ would be half empty of migrants if every little scuffle had to be taken into consideration.