While attending the school as both an undergraduate and law student, he played halfback for the Michigan football team for seven years from 1885 to 1891.

Although a swift runner and clever dodger his great strength lies in kicking ability, punting and drop-kicking.

[14] Prior to the 1888 football game between Michigan and Notre Dame, the players competed in a 100-yard foot race, which Duffy won.

On May 22, 1886, at a field day in Ann Arbor, Duffy drop kicked a football 168 feet, 7½ inches.

Outing magazine reported that Duffy's kick broke "the best record of the world by 11 feet and 5 inches.

Duffy, who holds the world's record for the drop kick, he having propelled the ball 168 feet seven and one half inches, at Ann Arbor May 22, 1886.

[3][4][5] With Duffy as captain in 1888, the team won its first four games, including two wins over Notre Dame, by a combined score of 126 to 20.

"[22] In Duffy's first six years as a varsity football player at Michigan, the team compiled an overall record of 17 wins and 4 losses.

While official sources list only Mike Murphy and Frank Crawford as the coaches of the 1891 team, the Chicago Daily Tribune reported in November 1891 that the Michigan team was "coached systematically" by Murphy, Crawford, Horace Greely Prettyman and Duffy.