The football game is mentioned in the novelization, but not in the film itself. In extended footage of the dinner table scene, cut from the final release, Marty Jr. yells "Fumble!" while watching TV, indicating that he's watching football.
In the novel, the Bears are described as playing in the "IFL", suggesting that the former National Football League has become an International Football League. By 2015, pro football is being played on Wednesday nights. (On September 5, 2012, life imitated art as the NFL actually began its season on a Wednesday night, departing from its traditional format of Sunday, Monday and some Thursday games).
The Bears were indeed having "their best season in 30 years", having won seven games and lost none as of Marty's departure from 1985. The most recent Bears' game when Marty left had been a win over the Packers on October 21, 1985, exactly thirty years before the game against the Spacers.