Duelinator

Win a duel without taking damage

You can do this on splitscreen, system link, or over Xbox-Live.

To start a duel, melee another player and they will melee you back to start the duel.

To do this just let one person attack the other while the other person does nothing. Then do the same for the other person. You must not receive "damage" but damage on the shield will not negate this achievement

The is best to do with a friend or over splitscreen, just do as said and beat them in the duel.