Threlfall played tackle for four years at Waltham High School in Waltham, Massachusetts. He enrolled at Purdue University in 1922, but financial difficulties forced him to leave. He returned to Purdue in 1923 and played on the freshman football team. He played tackle and center for the varsity team from 1924 to 1926. He was also a member of the school's wrestling team.[4]
Coaching career
During his senior year with the Boilermakers, Threlfall assisted coaching the team's linemen during spring practice. In 1927 he was hired as an assistant football coach at Bates College.[4] He and head coach Carleton Wiggin left after the 1928 season.[5] In 1930 he joined the athletic department at South Dakota State.[6] From 1934 to 1937 he was the school's head football coach and athletic director at.[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. His .778 winning percentage is the highest in team history.[8]
Insurance
In 1940, Threlfall joined the Winnipeg branch of Sun Life.[9] He then worked for the Great West Life Assurance Company. In 1953 he was appointed vice president and superintendent of agencies for Western States Life Insurance Company.[10]
Later life and death
In 1968, Threlfall retired and moved to Sun City, Arizona. He suffered a heart attack on February 3, 1971, and had a stroke six days later. He died on February 14, 1971.[11]