Joseph M. Duff Jr. (January 28, 1889 – October 10, 1918) was an All-American football player and coach who was killed in action during World War I. Duff graduated from Shady Side Academy in Pittsburgh, Pennsylvania before enrolling at Princeton University.

[1] He became a member of the Allegheny County Bar[2] and went to work in the law firm of his brother James H.

[3] In June 1917, he was in the Reserve Officers Training Camp in Fort Niagara, but was not given his commission due to a vision problem.

[2] Undeterred, he enlisted in the U.S. military in World War I and went to France as a private in the 313th Machine Gun Battalion,[4] 80th Division.

He was promoted to the rank of a lieutenant on September 30, 1918[5] and transferred to the 32nd Division to lead a machine gun company for the 125th Infantry.