The New York Yankees thought he was better at baseball, and Halas played right field for the team at the start the 1919 season until a hip injury and the curveball sent him to the minors. He loved to tell people he was replaced by Babe Ruth, a good story exaggerated by a time gap of one season.

Using his civil engineering college degree, Halas got a job designing railroad bridges, but his love for football led him to play in 1919 with the Hammond, Indiana semi-pro team with Driscoll and Jimmy Conzelman. Then and there, the always optimistic Halas said he believed in the future of pro football, even though his mother kept imploring him, "Go back to the railroad, dear. You'll have a steady income there."

An offer from A. E. Staley's starch company in Decatur, Illinois, lured Halas into taking a job that paid him to recruit and coach a company football team. The first player of note he signed was former Illinois teammate Dutch Sternaman. The Depression of 1920-21 caused Staley to downsize, and he offered Halas $5,000 to take his team to Chicago to advertise the name "Staleys" for one season. Halas gladly pounced before Staley realized his shortsighted benevolence. In 1921, Halas invited Sternaman to become a 50-50 partner before realizing he should have made it 51-49 to avoid a future problem.

"I was stupid, and I saved $100 a game because I didn't have to pay a player and a coach," Halas explained. Halas said he would have preferred Driscoll as a partner, but Driscoll was player-coach of the crosstown Cardinals.

In 1922, the Bears were born as bigger, meaner versions of Halas' beloved Cubs. Halas was negotiating to play for 50 years in what was soon named Wrigley Field. The Bears' shoulder pads fit Carl Sandburg's "city of big shoulders" perfectly, confirming Halas' instinct that a game of toughness would appeal to both urban and rural values of hard play following harder work.

As player-coach with Sternaman until 1930, Halas was a 6-foot, 175-pound end. He was named to the NFL's all-decade team, though Halas bragged about only one play—his 98-yard return of a fumble in Wrigley Field, the ball slipping free from Jim Thorpe of the Oorang Indians in 1923.

"The wet, muddy ball squirted from Jim's hands into mine. I sidestepped and took off. I heard an angry roar. It was Thorpe, coming after me. I ran faster, and faster, but I sensed he was gaining. I could hear the squishing of his shoes in the mud. When I could almost feel his breath, I dug in a cleat and did a sharp zig. Thorpe's momentum carried him on and gave me a few feet of running room. I zigged, I zagged. Zig. Zag. Just short of the goal, Thorpe threw himself at me and down I went, into a pool of water. But at the same time, I slid over the goal (legal at the time). No professional had run 98 yards for a touchdown. None did so again until 1972."