This achievement and Missed By A Mile are known to be glitchy. I was not able to get this one until later in the game when I kicked out the power and climbed over the ruined fence in Act 1. I was able to get this and Missed By A Mile on the same Taken. Others have had issues doing this on non-throwing Taken.
After wrecking the car and making your way to the lumber yard, and escaping the mobile home that is pushed into the ravine, kill the two Taken at the gate. Head right and turn left to see the breaker box. Go up to it, kick it, and walk over the fence. A Taken will appear in the distance.
He will throw something, hit LB and move in any direction. This should be 1. If not then just circle him and when he swings, hit LB. It should unlock. Then do this 19 more times.
Don't bother with the other non-throwing Taken since the achievement is known to be glitchy on them.