During the action phase, pictures D-F, the force of the arm, body and racket hitting the ball forward along with gravity pulling it downward, the ball's flight, although going forward is also going down.
(the force of the arm, body and racket; hitting; the ball; forward) (pictures D-F; pulling; it; downward)
the force of the arm, body and racket pictures D-F
hitting pulling
the ball forward
it downward