Halas was discharged soon after the Rose Bowl and reverted to baseball pursuits. He signed with the New York Yankees in March of 1919. Although he made a professional debut with that team on May 19, 1919, he played only eleven games and left a career record of meager statistics. As a right-handed batter he was extremely weak. With a batting average of .091, he never scored, nor did he bat in a single run. The lasting effects of a hip injury caused by a mishap during training camp in Jacksonville, Florida, in March 1919 further hastened his retirement from baseball.
He played briefly with a minor league team in St. Paul, until a contract dispute put an end to his career. Halas returned to Chicago for the duration of 1919 and worked as an engineer for the Chicago, Burlington, and Quincy Railroad. Turning elsewhere from professional baseball to satisfy his sporting interests, he joined a semi-professional football team called the Hammond Pros.
In 1920 he accepted an offer of full-time employment at the Staley Starch Works in Decatur, Illinois, where he served as athletic director and part-time coach of the company football team in addition to his full-time duties as a starchmaker. Despite his bad hip he spent summers on the company's baseball team and played right end on the football squad. His employer, A. E. Staley, provided generous support for the company football program, offering players a share of the gate receipts. Halas as a result met with success in recruiting a number of promising athletes from colleges nationwide. Among those early team members, the former Illinois halfback Ed (Dutch) Sternaman and Notre Dame center George Trafton hired into Staley's and played for the Staley Starchmakers.