The Los Angeles Rams of the National Football League (NFL) selected Lewis with the 200th pick in the 1946 NFL Draft, but NFL commissioner Bert Bell ruled him ineligible under league rules. The Rams took Lewis thinking he was in the 1946 graduating class, but he had one more year of eligibility left as an athlete who entered college in 1943. The decision delayed Lewis's professional career for a year; in 1946 he signed with the Cleveland Browns of the new All-America Football Conference (AAFC). Lewis started at quarterback for the Browns in their first three games in his first season, sharing duties with Otto Graham. After Graham took over as the starting quarterback, he became a defensive back who also returned punts and kickoffs. Lewis had five interceptions in his first season, when the Browns won the AAFC championship. Cleveland won the league championship in each of the ensuing three years before the AAFC dissolved and the Browns were absorbed into the more established NFL.