Would a Fight In Space Hurt Less?

The first punch might, because the assailant can’t brace against the ground, so some of the momentum of his fist will be wasted pushing his body backwards. But once the two brawlers are pushed in opposite directions to the walls of their spacecraft, they will be able to launch themselves back again. The second punch will be boosted by the forward momentum of the astronauts as they sail together, and it will hit even harder.