Allen's coaching journey began at the collegiate level, where he led teams at Morningside College and Whittier College. During his time as a head coach, he honed his skills and developed a reputation for his defensive expertise. His ability to identify and develop talent, combined with his strategic mind, set the stage for his future success.  

In 1957, Allen transitioned to the professional ranks, joining the Los Angeles Rams as an assistant coach. His contributions to the team's defensive schemes were instrumental in their success. He later served as an assistant coach and head of player personnel for the Chicago Bears, where he helped build a championship-caliber team.  

Allen's most significant impact came as the head coach of the Los Angeles Rams and the Washington Redskins. Known for his "Hail Mary" approach to the game, Allen emphasized physicality, discipline, and a relentless pursuit of victory. His teams were often characterized by their tough defenses and ability to make big plays. While he never won a Super Bowl, Allen's coaching career was marked by numerous successes and a legacy that continues to inspire coaches and players t

This legend entered the NFL as the LA Rams offensive ends coach and later served under George Halas with the Chicago Bears as :

✦ Consultant and Head of Player Personnel (1958)

✦ Assistant and Head of player personnel (1959–1961)

✦ Defensive Coordinator and Head of player personnel (1962–1965)

Allen went on to become the Head Coach of the Los Angeles Rams from 1966 to 1970 and again in 1978, and was the sideline boss of the Washington Redskins from 1971 through 1977.