So far I've managed to win all previous fist fights with the usual tactic: Block until the opponent tries a heavy attack, counter this and then beat the shit out of him until he blocks. Repeat until win.

Now the only opponent left is Valgard in Kaer Trolde and my tactic just doesn't work - because he almost never does a heavy attack. I've tried several times now and every time he did maybe 3-5 heavy attacks in 20 RL minutes - I got him down half his health maybe, but then I start losing patience. Once he was throwing quick punches for 15 fucking minutes! No way to get between those.
Is there some way to provoke him into heavy attacks? I tried hitting his block (most of the time this ends with getting hit myself) or varying the distance (because once it seemed like when I went away he would do a wind-up attack, but the next times he just closed the distance and continue his quick-punch-pounding).
Or is Valgard bugged?

Strange things happen...

I've tried this fight maybe 10 times and just couldn't get through because of those "always quick punches".
Decided to give it one last try about an hour ago... after I've written the question above. And suddenly the guy keeps swinging those heavy punches that are easy to counter and score hits on him after... Was a matter of maybe 20-30 seconds to defeat him. I'm still not really sure if that did it, but I indeed kept more distance this time. I don't know if that triggered Valgard not throwing only quick punches (tried that before but not as vehemently).
The fight against Olaf was super-easy in comparison. Now I'm on my way to find the Champion of Champions :-)