Imagine holding a basketball in both hands, throwing it straight up as high as you can, and then catching it when it falls. at which points in time does a zero net force act on the ball? ignore air resistance.

before throwing and after catching the ball

Explanation:

When basketball is in the hand of player net force on it zero as holding force is canceled by gravity Force. During its entire motion gravitational force is acting on the ball which is acting downward. Even at highest point gravity is constantly acting downwards.

After catching the ball net force on it zero as holding force is canceled by gravity force and ball is continue to be in stationary motion.