Answer:
The right answer is the following:
An unbalanced force causes the ball to stop.
Step-by-step explanation:
Assuming that we treat the ball as a point mass, we can apply to it Newton's 2nd law, at any time, and at any point in space.
So, we need to identify the external forces acting on the ball, once released from the kicker's foot, because they will define the movement of the ball.
In absence of any unbalanced force, the ball must remain moving forever in a straight line at constant speed.
In the vertical direction, we have two forces; gravity (always downward) and normal force (perpendicular and upward regarding the surface on which the ball is rolling; if we assume that the field is level, it's directly upward).
As there is no movement in the vertical direction, we can write the following equation for Newton's 2nd law applied to the vertical direction (choosing this direction to coincide with the y-axis):
Fy = Fn- Fg = 0
In the horizontal direction, the only force acting on the ball (assuming rolling without sliding) is the static friction force, which produces a deceleration on the ball until finally it comes to an stop.
This force meets the Newton's 2nd Law for the horizontal direction (which we identify as our x-axis), as follows:
Fx = -Ff = -μs*Fn = -μs*m*g = m*ax ⇒ ax = -μs*g, where μs= static coefficient of friction between the ball and the field surface.
This unbalanced force, causes the deceleration which, as a consequence, stops the ball.