In 1963, Cassidy, from Levittown, Long Island, New York, scored a one-punch, 39-second knockout in his professional debut at Sunnyside Garden.
Among the notable fighters that he defeated were Don Fullmer, Jimmy Dupree, Tom Bethea, Isaac Logart, Ramon Ranquello, Tommy Hicks and Christy Elliott.
He also fought world champions Luis Manuel Rodríguez, Rodrigo Valdez and Alessandro Mazzinghi.
The Dupree fights were part of stretch during which Cassidy fought eight consecutive opponents ranked in the Top 10.
The cast has featured several former boxers, including John Duddy, Seamus McDonagh and Mark Breland.