[2] Threlfall was the head coach of the Winnipeg Blue Bombers of the Canadian Football League (CFL) from 1938 to 1944.
He enrolled at Purdue University in 1922, but financial difficulties forced him to leave.
[4] During his senior year with the Boilermakers, Threlfall assisted coaching the team's linemen during spring practice.
[7] From 1938 to 1942 he coached the Winnipeg Blue Bombers to 28-8 regular season and five Grey Cup appearances, winning in 1939 and 1941.
In 1953 he was appointed vice president and superintendent of agencies for Western States Life Insurance Company.