Tomb Raider: Underworld

When you come across an enemy while you riding the motorcycle simply stop the bike and press B + RT then left or right on the left stick to power slide in a circle, the enemy will try and attack you and get hit by the bike while you are spinning around, a couple of hits is all it takes to take them out, hope this helps

This one can be a little tricky since the motorcycle usually doesn't do enough damage to take out an enemy in one pass; you have to keep circling around and hitting them again. If you're having trouble, try whittling down your enemy's health with your guns first, then hopping on the bike and finishing them off. As long as that final blow is from the bike, it counts for this achievement.