Disclaimer: I don't have a Master's degree in Viking or Norse fighting techniques.
Now that that is out of the way....
When i was stationed in germany, I took a few courses on Military Science for my OTC, and one of them had a little bit about various fighting styles throughout the ages. Now, the Vikings pretty much forged the world as we know it today, so there is a lot about them.
Apparently the style I mentioned above (in brief) was used like this: BIG TWO HANDED WEAPON. The warrior with the big two hander would hack, spin, hack, spin, very very fast in a berserker state, smashing through enemy troops, not standing or prancing around, fighting this way in a straight line, until he died, or broke through the enemy lines, then he would turn around and do it again until he was back to his lines.
For a good example of this, check out the Highlander episode where Duncan Fights Kanwulf (Kanwulf uses a two handed axe with a shield strapped to his back, does a lot of spinning, catching Duncan's claymore on his shield numerous times).
The scots and irish learned to fight this way by copying the vikings (and the scots claymores were much bigger than most viking axes)