(a) When a football is kicked into the air vertically upwards, as shown in figure the motion of body is under gravity and no any external force acts on body so acceleration of the football will always be vertical downward and is equal to $g$.


Hence, the direction of acceleration is always towards the centre of earth i.e. downwards.
(b) If the football thrown vertically upward, when it reaches the highest point velocity $\left(v_y\right)$ will be zero as it is continuously retarded by acceleration due to gravity $g$.