Try this:

Stand on one leg.
Throw a weight ball (only 2kgs in my case) at a very tight trampoline-lookin-thing up on an angle.
Catch the ball as it comes whizzing back at you at about three times the speed at which you threw it.

Did you get smacked in the face too? Or did you just fall down?

Anyway, that's my new favourite exercise at PT. Someday I'll graduate to doing it on one leg *while* standing on an inverted half-ball.

I'm going to be very very sore tomorrow.