Need for Speed Rivals

To obtain this achievement you need to bust a racer with an 8, 9, or 10 above his car. I have only seen a max of heat level 5 on the A.I. racers that drive around. So this must be obtained from an actual player playing as a racer in a multiplayer game.

Alternatively if you're patient, it can be obtained by the very last assignment for the cop career which is an Interceptor mission with a heat level 10 racer. (I used a level 4 EMP and ESF which took him out pretty fast.)

EDIT: If you want to know the easiest way to get this achievement, look at Reborn Insanity's solution. If however you want to get it earlier, follow the solution below:

As soon as you start to see heat level 5 racers in free roam (should be around rank 10 if I remember correctly) enter a Hard Hot Pursuit event. Let at least one racer cross the finish line. You won't get gold for the event, but his heat level will skyrocket, usually to eight or higher. Bust him to get the achievement.

If it doesn't unlock, try it again - it might not work first time. It might be worth pointing out that when I did this, only one racer crossed the line, and he had remained first throughout the whole event. I also lowered his health a little bit during the event, to make capturing him after a lot easier.

My solution is very simple and this is a given if you have played through the cop story.

1. Finish the story up to zero hour hot pursuit!

2. Get ready for some fun and make sure to have a fast car with some good pursuit tech.

3. Be ready to take some pursuit hits, so most likely go with the bugatti for the last race.

4. Zephyr has an automatic heat 10 tacked on to him. This achievement is inevitable if your patient. Have fun!

Take care,
Eklebtik

The easiest and most fun way to obtain this achievement, in my opinion, is to do it with a friend. Enter a friend's world, playing as a cop, with them as a racer. Find a repair station in an open area (there's one in the south-western desert area near the 1-4 Golf Camera that works particularly well), start a pursuit with your friend, and get ready for craziness.

As more cops join the pursuit, make sure you and your friend stay in close proximity to the repair station, healing as needed. I recommend that the racer equip level 4 Shockwave and ESF for maximum damage against rival cops, boosting their heat level faster. Once they reach heat level 8 (or 10, if they still need the 10 Heat Achievement), have your friend let you bust them, netting you this achievement.