You throw a basketball by exerting a force of 14 newtons. according to newton's third law, there is another 14 newton force created in the opposite direction. if there are two equal forces in opposite directions, how does the ball accelerate?

Newton’s Third Law describes two different bodies acting on each other.
now you've considered the action and reactions based on d ball, but have u considered the force the athlete exacts on the ground which is external to the athlete-ball system, now the ground in which the athlete stands exert a force back on the athelete-ball system which causes the ball to accelerate