Erasmus was drafted with Fremantle's second selection, the 10th overall, in the 2021 national draft. He made his AFL debut for Fremantle in the Western Derby in round 3 of the 2022 AFL season, collecting 18 disposals.[3] Erasmus was among Fremantle's best during round 18 of the 2023 AFL season against Collingwood at the MCG, collecting 26 disposals, 12 contested possessions and 10 tackles.[4] He finished his second season at Fremantle having played fourteen games.
Erasmus was awarded the Simpson Medal as the player adjudged fairest and best in the 2024 WAFL Grand Final.[5]