Joseph M. Duff, Jr 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. He played guard for Princeton and was selected for Walter Camp's All-American eleven in 1911. After graduating from Princeton, Duff became an assistant football coach at the school for the 1912 football season, assisting head coach Logan Cunningham. He served as the football coach at the University of Pittsburgh in 1913 and 1914 and graduated from the School of Law in 1915. He served in the U.S. military in World War I. He went to France as a private in a machine gun unit and was promoted to the rank of a lieutenant. He was killed in action in France on October 10, 1918.