I'd heard of O'Malley's comics but hadn't read them before watching Wright's movie. So at the moment of confrontation, I figure: Okay. Either Knives or possibly Ramona will have to teach the dweeb to fight, so that after a standard sequence of bungled training he will at last transcend his inadequacies and assert his rights as a man. In the next instant I stood corrected. Scott Pilgrim knows perfectly well how to fight. He has superhuman strength, speed and leaping ability, as do his antagonists. He is both a dweeb and a superhero. This is possible because he exists in a video game universe where he can accumulate points with every well-struck blow toward earning an extra life (he'll need it), where Knives and Ramona in fact do have super fighting abilities (and Ramona carries a giant retractable sledgehammer in her handbag) and where defeated enemies explode into clouds of coins.
For all I know, anyone in the movie could fight like the main characters do, but most of them don't need to. That's because the fights are metaphors the way Astaire and Rogers's dances are metaphors, the latter for courtship if not consummation, the former for the modern struggles of lovers with one another's baggage of past but perpetually present exes. It may sound blasphemous to compare the work of Michael Cera's stuntman with the lyric agility of Fred Astaire, but the fight scenes and the dance scenes serve the same basic narrative purpose.