The correct statement regarding the relationship between the net force and the ball's movement is:
The net force causes a decrease in acceleration because without the force the ball's velocity would remain the same.
In this context, we need to remember the relationship described by Newton's second law of motion, which states that an unbalanced (net) force acting on an object causes the object to accelerate (change its state of motion). When a nonzero net force acts on the moving ball in the opposite direction of its motion, it will decelerate (decrease in velocity), effectively causing a decrease in acceleration until it comes to a stop.