O'Brien faced controversy when he accidentally tweeted that West Coast ruckman Nic Naitanui is "lazy and unfit", attributing the mistake to a broken smartphone.[8] Naitanui responded jestfully by gifting O'Brien a new phone after that weekend's game between their clubs.[9] A stand-out in Adelaide's least successful season in their history, O'Brien thrived at every opportunity, winning the Malcolm Blight Medal in just his first season as the primary ruck. His fantastic form was rewarded with a contract extension to keep him at Adelaide until 2025.[1]
In 2023, with Riley Thilthorpe as his back-up ruckman, O'Brien lead the competition for hit-outs.[10] Part-way through 2024, the struggling Crows chose to drop O'Brien to the SANFL in favour of Kieran Strachan in an attempt to revive the club's season.[11] O'Brien returned after two games on the sidelines, and still led the competition for hit-outs and average hit-outs by the conclusion of the season.
^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.
Personal life
Outside of football O’Brien has completed a medical science degree at Flinders University. He has since undertaken post graduate study, both in business administration and public health through Torrens University.[13] He has also completed postgraduate study in neuroscience through King’s College.[14]
O’Brien graduated from high school with an ATAR of 99.75.[15] In 2024, O'Brien won the league-wide Jim Stynes Community Leadership Award for his advocacy and community work for mental health in South Australia.[16][17]