This requires you to get 3 stars on all events in the different tiers. As for the cop ones, be prepared to return to previous races with better cars to get those three stars. Especially the final race in tier 4 is extra hard. To 3-star it, you need to finish the race with 20 or more seconds left on the clock. Use all your powerups when they are available, especially overdrive. I also suggest using nitro on straight sections or if the police car is just about to overtake you. This may require several attempts, so good luck!