First you must buy the "Arrow Deflection" skill (level 3/3) in the combat skill tree. Now you must look for some archers and parry their arrows just a moment before they hit you. A great spot is at the eastern bridge of Oxenfurt. There's a fast travel point and some archers on the bridge. After killing them you can meditate for an hour and they should respawn. Repeat until the achievement unlocks. Here is a video, credit to PowerPyx, to aid you: