Dreaming of playing a sport by yourself is the manifestation of the pride in your own successes. Sports is a form of exercise, but even more so, sports are a competition as well. Dreaming of sports is that envisioning of your pride, of thinking well of what you have accomplished physically.
This dream can mean that you have lack teamwork with others and need to work on restoring that. You have a tendency to only believe in your abilities, but refuse to acknowledge others. Try to trust others and allow them to work with you before writing them off.