The Nose Crusher.

Not too impressive for a guy demonstrating his trust in physics, note the fact that he still flinches when the ball comes towards him. I would expect the guy to be like a rock.

My physics prof at Rice did this demo every year until a disgruntled student in the front row (who had just failed his physics test the previous week) stood up and gave the ball a tap on it's way back to the prof. Breaking his glasses and bloodying his nose.
Now he no longer stands against a wall in case anyone "helps" the ball again.