For the first of the three archery challenges, Artemis told them to shoot the smallest branch on the tallest tree in the forest. Centauride came very close, but Stag managed to hit it because of his bow.
For the second challenge, Artemis sent them after her swiftest boar and instructed them to shoot it in the heart and kill it. After several days of hunting, Centauride managed to shoot it in the leg, but after it was slowed Stag shot it in the heart and killed it.
For the last challenge, Artemis plucked a single hair from one of her hunting dogs and placed it on the top of the tallest mountain near the forest, instructing Centauride and Stag to snap the hair in half by shooting from the bottom of the mountain. Despite the challenge, Centauride hit the hair. However, Stag managed to snap it in half, meaning he won the challenge. However, unbeknownst to Stag, it hadn't broken quite yet.
As Stag boasted about his victory, Artemis congratulated him and encouraged him to shoot Centauride in the shoulder to mark his victory. Though she ran away, Stag struck her in the shoulder as instructed, and directly afterwards, the hunting dog's hair snapped. The competition had officially ended, and Stag had cheated by shooting his opponent and therefore lost.
Stag should have been killed for losing, but Artemis had pity on him, instead turning him into a horse and removing his mane and tail to humiliate him as punishment.
She let him keep his crown, but removed the gold and melded the willow branches to his head, becoming horns. She told him that as eternal punishment for his foolishness, him and any children he had would be game for her hunters to shoot for all eternity, and they would be called "deer", meaning small creature, to remind him that he is tiny compared to the gods. She then healed Centauride's arm and granted her a new crown, and banished Stag to the forest. To this day, Stag's many children roam the forest as game for anyone to hunt, eternally living out their father's punishment.