Basketball is a very physically demanding sport.
Running up and down the court; getting low for the proper defensive stance; executing offensive moves effectively; making proper passes.
It is enough to deplete most people's energy.
I played on Saturday afternoon right outside the Anteater Recreation Center.
It was the hardest I played in a while. I felt intense fatigue during the course of one full court game after I had dribbled down the court and tried to drive in for a lay-up.
It's beneficial for my physical and mental well-being, though.