This achievement requires that you kill an enemy with a throwing knife that has ricocheted off of a surface beforehand and can ONLY be earned in CAMPAIGN. You will first need to purchase a pack of throwing knives (5 knives for 1,500 credits). Once purchased, the throwing knife button will replace the grenade button on your HUD. There is no specific location for easily obtaining this achievement. You just need to find a single enemy to attempt this achievement on. Make sure you are playing on easy, get relatively close to them and line up your cross-hairs on the ground in front of the enemy (with Aim Assist on, this may be a challenge, turn it off from Pause Menu under Options if you need to). Hit the knife button and the knife should bounce of the ground in front of the enemy and then hit and kill them. If you're fighting with other allies, be quick as they often kill the enemy while attempting to line up your throw. This may take a few tries but overall it is quite easy to do.