Olaf was excited, even more so seeing just how tense Ulfric was. It made it clear it was going to be another tough fight- he was not going to sit around and play it safe when the atmosphere was so thick with emotion. It would probably spell his death!
When the male attacked, Olaf responded by jumping back, landing squarely before charging forward. However, he hadn't managed to jump back as much as he had thought, and didn't have enough room to raise a paw in counter attack. Already moving, all he could do was plow forward and slam his head against the other's in a very strong headbutt.
Stumbling slightly, he shook his head, trying to blink the spots from his vision. Alright. Maybe he needed to be a little less eager and actually think about his moves.