Stager began as a leading high school swimmer at Newark Academy in Newark, New Jersey. Competing on the U.S. Army team from the Philippines, Stager won the 400-meter free-style event at the "Pacific Army Olympics" held in Manila, Philippines in December 1945. He enrolled at the University of Michigan after being discharged from the Army and set a freshman American record in the 200 yard free style in February 1947 with a time of 2:12.3. He went on to become a three-time NCAA finalist, and named to the coaches' All-American team every year he swam for the Wolverines. In 1948, he swam for the Michigan Wolverines team that won the NCAA swimming championship.
