Career
The red-headed O'Brien used to make 10-hour return car trip to Glenelg to play under-15 games. At 16 he played in his first West Gambier senior premiership in the Western Border league. He has a terrific mark and good leg speed, where he recorded the third-best result in agility draft camp.
Hawthorn selected O'Brien with pick 28 in the 2012 AFL Draft. Entering into his second season, O'Brien changed from number 40 to Hawthorn's famous number 23 jersey following Lance Franklin's move to Sydney at the end of the 2013 season.