NOT The Outsiders. Probably takes place in the 70s or 80s. Near the end of the movie there is a big rumble between two groups. Fighting for one group is an older man, maybe in his 60s, who has worked out a lot at various times when he is shown briefly throughout the film. He punches his son really hard in the stomach right at the end of the rumble because he is so pumped about winning even though they are on the same team. The son was a main character. I believe the rumble took place at a high school football stadium during the day.