Even after years playing football, David Striegl had never got into a fight - until he was knocked out cold by a rogue kangaroo.

Mr Striegl, 25, was running up Canberra's Mount Ainslie during his lunchbreak on Thursday and did not think twice when he spotted one of the resident roos nearby.

The bushland reserve in the nation's capital is popular with joggers and cyclists, and assaults by the marsupials who share the mountain are rare.

Mr Striegl was knocked unconscious and remembers little about the attack.

"I turned around and before I knew it, it took a swipe at my face," he said.