Harrison started his playing career back in U10's with the Solihull Barons Hockey Club. He would then progress through right up until U18's, in a season he was assigned the Assistant Captaincy. Sumner also iced in four NIHL1 games and four NIHL2 games in his last season as a junior in Solihull, playing for the Blackburn Hawks and the Milton Keynes Thunder.
Sumner would make the move to Coventry for his last season as a junior post the pandemic. Since the 2021-22 season, Sumner has iced for the Coventry NIHL Blaze full time.
In the 2023/24 season, Sumner would lead the team in goals with fifteen in twenty-nine regular season games and also pick up the Player of the Year award.