This prompt has limited use. The idea is to take two sports and combine then to create a brand new sport. It works well for fantasy and science-fiction when you want to develop a society different from our own. Place the sport you created at the center of the story and develop the society which would play it.
Keep in mind that sports movies are about more than just the sport. They provide a setting for the people who play and manage the sport, the people watching the sport, and the sponsors. That gives plenty of plot possibilities to explore.
Here are five sports match-ups.
Football and soccer
Baseball and dodgeball
Bowling and track
Basketball and volleyball
Swimming and boxing
Based on football and soccer I generated this pitch.
Ball - Touted as the ultimate team sport they just call it Ball. Some think of it as a mangled version of volleyball, soccer, and dodge ball. Allen just considers it awesome. He is on the fast track to becoming the first Ball player drafted out of high-school. The big teams are wooing him to sign when he is contacted by a government rep to play for the National team. But when he signs with the Nationals he finds out that it isn’t a game at all. The government is using the sport to influence the minds of the country’s citizens. Now Allen has to choose between playing along and becoming the greatest Ball player of all time or destroying the very game he loves.