Here's why:

* Projectile definition: A projectile is an object that is thrown or launched and then moves under the influence of gravity alone.

* Ball on the ground: A ball on the ground is at rest. It's not moving and not subject to the primary force of gravity. It's being held up by the ground, preventing it from falling.

To be a projectile, the ball would need to be:

* Launched: It needs to be thrown or propelled upwards or horizontally.

* Moving: It needs to be in motion.

* Affected by gravity: The only force acting on it should be gravity.

Example: If you kick a ball across the ground, it's briefly a projectile until it hits the ground again.