A men's ball is about 9.55 inches (24.26 cm) in diameter and a women's ball is about 9.23 inches (23.44 cm) in diameter. The metal rim of the basket hoop is 18 inches in diameter, which is about double the diameter of the ball itself.

We would like a formula for the area in which the center (centre) of a vertically falling spherical ball (of diameter d) has to be in order to pass cleanly through a circular hoop of inner diameter D.

To be clear, the ball must not hit the sides of the hoop.