How do you say in Finnish:

"I have already fought Helsinki rockers?"

Olen jo tapellut helsinkiläisten rokkaajien kanssa - assuming that the
fight was just a general scrap and not an organised fight such as at a
boxing match and that by rockers you mean rock 'n roll fans who dress
in a certain style...

Certainly, a sentence worth keeping in mind when travelling to Helsinki.

Dear steveinfinland,

Thank you for the help. This is exactly what I meant.