Ewbank grew up in Indiana and attended Miami University in Ohio, where he was a multi-sport star who led his baseball, basketball and football teams to state championships. He immediately began a coaching career after graduating, working at Ohio high schools between 1928 and 1943, when he entered the U.S. Navy during World War II. While in the military, Ewbank was an assistant to Paul Brown on a service football team at Naval Station Great Lakes outside of Chicago. Ewbank was discharged in 1945 and coached college sports for three years before reuniting with Brown as an assistant with the Cleveland Browns, a professional team in the All-America Football Conference (AAFC). The Browns won all four AAFC championships. They joined the NFL with the leagues merger in 1950, winning the championship that year.