Oscar attended Ringwood Secondary College in Melbourne's east, graduating in 2012.

McInerney was recruited to the VFL club Casey Scorpions for 2016, as a 204 cm ruckman, quickly making an impression with his ability to cover the ground, accurate tap work and clean hands below the knees.

Winner of the A. Todd Medal for the best player in the VFL Development League, McInerney featured in the Scorpions’ VFL Finals campaign and attended the NAB AFL State Combine.

Making his debut in round 2 of the season, McInerney was impressive with 21 possessions and four inside 50s.

Finishing second on the NEAFL ladder that year, McInereny was a crucial part of the Lions' finals campaign, being listed among the best players on the ground in their semi-final match up against Sydney University.