The Universal Law of Gravity is stated symbolically as:
F(gravity)=m₁•m₂/r²
Essentially, the gravitational attraction of two objects is proportional to mass of two objects. This means that as the mass of objects increases, the attraction of gravity also increases.
So, the basketball has a fairly light mass, as it is filled with air. When the kid exerts a net force on the ball, the ball will accelerate until it reaches a point when gravity overcomes the kid’s net force. From here, gravity is trying to pull the basketball down towards the center of the Earth because gravity produces a greater net force and breaks the ball’s inertia. Because the gravitational pull is strong upon objects on Earth, the ball instantly falls towards the ground. Even though the ball does not have a whole lot of mass, it’s distance to Earth’s center is insignificant compared to objects such as the sun or moon because it has a much shorter distance. So, the ball is still pulled down towards Earth.