Lahr began as a reserve player under Western Reserve head coach Tom Davies in 1942, when he was a sophomore. He played halfback for the Western Reserve Red Cats. His college career was interrupted, however, by three years of service in the U.S. Navy during World War II. Lahr returned to Western Reserve in 1946 and had a successful junior season as a left halfback. The Red Cats went undefeated against the three other rival Cleveland schools of the Big Four Conference, and Lahr was named to the 11-member All-Big Four city all-star team after the season. He also won the school's Jack Dempsey Adam Hat trophy for his performance.