On the map you will see some skull icons. This means at that point there is a Death Run.
Get up the stairs and choose the challenge (I suggest to take the left picture).
Complete all the Skull icons (after you complete succesfull there is a gastank icon on it) and the trophy is yours.
TIP: You can play fair an square. But this is the wasteland and only what matters is that you screw this guys up. So take your gun and shoot at the gas tank on the car. Its makes it alot easier for you.