UT consists of 10 races, and you have 3 lives to beat the whole Tournament. The better your car, the higher the entry cost, but the prizes also improve. To enter the Underground Tournament, your current car must have a particular best time that may vary for each car and distance.
In this mode, you choose each of your opponents yourself out of 4 presented. You can also use some illegal boosters that are only available in this mode: Race Fuel, Illegal Tires, Extra Bottle of Nitro, and Instant Launch. The first two increase your car’s stats, the extra nitro will give you more nitro time, and Instant Launch will allow you to bypass the traffic lights at the start and launch into the race automatically.
All of them will give an extra edge over your opponent, and using them will allow you to win some races that seemed impossible before. You can purchase these boosters right before the race, or get them from the crates and as prizes after your UT finish!