Average acceleration is defined as:

.

In words, this definition indicates that the acceleration is equal to the rate at which the velocity is changing.  Since  is a positive scalar, the two vectors in the definition,  and , have the same direction. 

Point D is a turning point, hence the velocity of the ball at point D is zero.  Consider a small portion of the motion with an initial point at point D and a final point just after point D.  Since the velocity at point D is zero,

 =

You indicated that the direction of the acceleration at point D is 8.  Since  and  have the same direction, and since , this means that the final velocity of the ball (i.e., the velocity just after point D) is also in direction 8.  Is the ball really moving in direction 8 just after point D? 

Brief Help Theory