However, that wasn't so much great acting as actual physical pain -- while kicking the helmet, Mortensen broke two toes and fell to his knees, not because the script required it, but probably because he simply couldn't stay on his feet anymore.
Lord of the Rings: Behind the Scenes
And that's why Aragorn is in a mobility scooter for the rest of the movie.
But hey, who needs toes? It's not like someone threw a knife at his face or something -- nope, that happened in The Fellowship of the Ring, when another actor misjudged a throw and accidentally flung a real knife at Mortensen's face at high velocity; according to the DVD commentary, Mortensen managed to swing his sword and block the knife, creating another unintentional badass moment for his character.
His role as a baseball player in that shitty Sandra Bullock movie saved his life.