Dadmun was born on June 25, 1894, in
Cambridge, Massachusetts. He played
college football at
Tufts College. After two years, he transferred to
Harvard University. In 1916, he was elected the captain of Harvard squad. That year, Dadmun was named first-team All-American by
Walter Camp,
Walter Eckersall, and
Fielding H. Yost and second-team All-American by the
United Press and
International News Service. He graduated in 1917 and joined the
United States Navy. He served in France during
World War I and was discharged with the rank of ensign. ==Professional football==