He was selected by the Detroit Lions in the 19th round of the 1948 NFL draft. The New York Yankees of the AAFC also recruited Hafen, but he signed with the Lions in January 1949. He played for the Lions during the 1949 and 1950 seasons and appeared in a total of 24 NFL games. While with the Lions, he trained in the off-season by "bull-dogging and roping cattle" on his family's ranch in Utah.