Asphalt Legends Unite

I will admit I'm not 100% certain what a perfect run is, but I can say for sure that you don't need to finish an entire race without hitting anything, or anything like that. It seems to be that each time you travel a set distance without hitting anything, you'll see a little "Perfect Run" bonus pop up on the right and you'll get extra nitro for it.

To put it in perspective, I unlocked this achievement after my second race ever in this game. You will be doing this literally thousands of times throughout your time with this game.