Oates played five seasons with the Etobicoke Eclipse of the Ontario Lacrosse Association (OLA) Junior A Lacrosse League. An offensive standout, Oates' total of 181 points in 19 games in 1981 was the 11th highest total in OLA junior history at the time. As the league's leading scorer, he won the Bobby Allan Award and in one game that season, set OLA Junior A single-game records of 19 assists and 29 points. Oates played one season of Senior A with the Brampton Excelsiors of Major Series Lacrosse but left the game in 1984 to focus on his hockey career.