The Cubs were ready to release him at the end of spring training 2019. They thought they had better talent ahead of him in the outfield. But they offered him a chance to stick around if he'd immediately switch and become a pitcher.
Coincidentally the story of the film is about an aging Detroit Tiger who is attempting a Swan Song season and make it to the World Series. This is of course what happened the very next year, as the Tigers would go on to be World Series Champions.