To successfully pass the mission, disable the perp. To earn a commendation, stop him by stressing him out and get 50% or less damage. As soon as the mission starts get on the freeway and drive until you see the car thief coming in the opposite direction. Quickly pull a quick U-turn at the next break in the median strip and catch up to him as fast as possible. Quickly disable him by continually ramming him until he stops driving. Remember to keep an eye on your damage meter so you don't wreck your vehicle before disabling the perp.