Easy with a second controller. Host an online game with two controllers. Turn AI off. Crashing into another player does I believe 11 damage to their car. Once the race starts grab the second controller and drive it along the wall to do a good amount of damage. Once the car's health is around maybe 15-20, grab your controller and crash into the second car once it's else is below 10. Attached is a video of me getting the achievement.