Alternate Ending: The Junior Novelization has one, in which the Road Runner comes in and scores the second-to-last points of the game instead of Bill Murray. Likely because no young reader will know who Bill Murray is.
Reality Subtext: Michael Jordan did indeed return to basketball after a stint at baseball (where he was set to retire into at the time) and led the Chicago Bulls to victory on his first game since retiring! In reality, there were sliiiiiiightly less Tunes involved.
Well, one could argue that practicing basketball so he could shoot gameplay scenes with proper verisimilitude was what helped get Jordan back into shape for un-retirement.
What Could Have Been: Joe Alaskey said in an interview he initially expressed interest in voicing some of the Looney Tunes for this film (or at the very least, provide Daffy's voice). But, despite the fact that Alaskey had several years of experience doing spot-on renditions of Mel Blanc's characters, producer Ivan Reitman kept making him audition several times, and flip-flopping back and forth as to whether or not he should be cast. Alaskey finally got fed up and said, "Look, either you want me, or you don't!" Alaskey didn't hear from Reitman again after that. In the end though, Alaskey admitted he was glad he wasn't involved in Space Jam after actually seeing the movie and realizing it was a terrible film.