Oscar attended Ringwood Secondary College in Melbourne's east, graduating in 2012. After leaving school he played local football for Montrose in the Eastern Football League. 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.
AFL career
After being drafted to the Brisbane Lions, McInerny began playing in the NEAFL for the Brisbane Lions reserves. Making his debut in round 2 of the season, McInerney was impressive with 21 possessions and four inside 50s. In Round 10, McInerney managed 46 hitouts and four goals. 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. McInerney was part of the Lions' NEAFL premiership, as the Lions went on to defeat Sydney by 3 points.
^The 2020 season was played with 17 home-and-away matches per team (down from 22) and 16-minute quarters with time on (down from 20-minute quarters with time on) due to the impact of the COVID-19 pandemic.