1: Make sure that you're in a map with "the saw"(shooting disc) as a weapon, and have enemy's in your mission. Forestry is a perfect map. Only saw-drops here

2: Start the game and make sure you have "the saw" on your car as a weapon.

3: Once a enemy hits YOU with the saw, you spin around for around 4 or 5 times.

4: Within these spins, this is the time for you to shoot the saw, and hit a enemy with it. Only hitting is not enough, you need to kill them too! (You need to be spinning in circles in order to get this achievement. Aim well. Just make sure you hit a enemy when he's near a corner so he will fall to death. This counts as a kill.)

Congratulations! Achievement unlocked!