Gauntlet Runs are single lap races in the game. You will only need to win 2 of these for the trophy to unlock. The first is found southwest of the west entrance to your base. It is right next to one of the campfires. After completing the race, the next event will be added to your quest log and is found along a beach in the southwest.
During the race you can shoot racers in front of you with your bow or use your spear on racers next to you to slow them down. You can pick up additional ammo and tools hanging from beams with
. Tools can be used with
. The Blaze Boost will give you an extra boost of speed.