The forces acting on the ball are the weight of the ball and the reaction force. The weight acts vertically downwards while the reaction force acts vertically upwards. These forces are equal in magnitude and there are no external forces acting on the ball. The ball is in equilibrium and will continue to stay at rest.
When a body is in equilibrium it will either stay at rest or move in a straight line at a constant speed unless acted by an external force.
The net force acting upon the ball is directly proportional to the acceleration of the ball and the direction of the force and acceleration are the same. Therefore, if the net froce increases the acceleration of the ball increases.
The basketball exerts a force on the ground and the ground exerts an equal and opposite force on the ball. This causes the ball to bounce up again.