Well, sports are part of self improvement. They not just exercise the body, but the mind too. A sport can improve our willpower, tenacity, or even teamwork, leadership skills, like planning, coordinating, etc.
Swebernd opened a thread with a video I watched since then. It is a good video, not because of the revolutionary thoughts in it, but for the sum of what's already been said, and the easy to understand explanation. I'll delete the thread, but here's a screenshot of it, and the link he shared.
https://youtube.com/watch?v=B9XGUpQZY38 [Embed]