Roundabout

Two options/locations to accomplish this challenge:

1) Area One: Far East portion of the map
2) Area Three: Fair Ground

The Fair Ground derby is a slightly larger arena, but I didn't have much difficulty in either location to reach the 8 cars.

During the derby, you need to beat 8 police cars. It's not ridiculously difficult since the cars come at you one at a time, so you just need to know the car patterns and how to beat the police cars. Here are some simple strategies to use:

Car Patterns:
1) Area One: 4 Red Cars - Each has their own circles
2) Area Three: 4 Red Cars - Each pair of cars has small figure 8/ellipse pattern

Police Car:
Police cars will aim to hit you and don't have the greatest turn radius. The important thing to remember about them is that as soon as they hit something (wall or red car), they will bounce right back. Therefore, try to get away from the trap you set so they don't bounce right into you.

Limo Strategy:
I did this without the shrink power-up, but it could make it easier to get out a jam if you're having difficulty. In general, be inside or near the circles created by the red cars. When the police car gets nearby, you'll want to jump out of the way (or drive out of the way) and let the police car hit the red car. When jumping, consider holding the right trigger to accelerate and move further away. If you get lucky, you might get the police car to ricochet back and forth and beat it on trap.

The key is to never rush yourself. There isn't a time limit during the challenge so just aim to get each car one by one even if that means one hit at a time.

Achievement unlocks after the challenge is complete, not once you get your 8th knockout.

I had difficulty constantly trying to bait and switch the cop cars in front of the red cars. This works much better if you don't use the red cars on the sides at all. Instead, bait the cop car to the bottom left or right. Before the cop hits you jump to the opposite side. The cop will hit the wall and bounce back towards you. The cop cars have a large turn radius and you have plenty of time to jump back to the original side.

Basically you will just jump from left to right while the cop cars bounce in half circles. Doing it this way you put yourself in much less risk and make the movement of the cop car much easier to predict.

Here's a video of me doing it for a while:


Leave some comments if you have some more ideas, or concerns.