At Ohio State, Hartline built a resume few assistants can match. After returning to his alma mater, where he starred as a receiver from 2005–2008, Hartline climbed the coaching ladder from quality-control assistant in 2017 to WRs coach, and eventually offensive coordinator. Under his guidance, the Buckeyes offense consistently ranked among the nation’s best. In 2025 alone, they finished top-25 in scoring (37.0 points per game), total offense (438.5 yards per game), and passing (267 yards per game), with standout performances from players like quarterback Julian Sayin and receiver Jeremiah Smith.