When done correctly, light and shadows create drama in a figure. Grief, sadness, evil glee and evil thoughts, can be represented just by the proper use of light and shadows.

Knowledge of the facial features and their subtleties, as well as the knowledge of how light behaves when passing through the face is important Shading technique is somewhat difficult to master, but like everything else in drawing, everything can be perfected through constant practice (and with the aid of proper references, of course).

Once you've learned these things, you will be able to draw figures with drama and atmosphere and induce strong emotional responses from viewers.

Try drawing the ball first and seeing how you do. Then once you've done that a few times try the arm.

Don't forget to use shapes first when creating the arm! Again follow the process and add details at the end. The very last thing is then the shading.