 Between 1985 and 1990, Cassidy would spend most of his time in the Black Hawks' minor league system, playing with the Nova Scotia Oilers of the American Hockey League (AHL), the Saginaw Generals of the International Hockey League (IHL), the Saginaw Hawks of the IHL and the Indianapolis Ice, also in the IHL.Cassidy's NHL playing career was limited due to his knee surgeries.He would also play 36 games with the Blackhawks during those years, scoring 4 goals and adding 13 assists for 17 points, along with 10 penalties in minutes.