Unsupported standing, reactive balance bouncing a ball against a wall (Balance, standing, throwing/catching ball against wall - with variations)

Stand up straight in front of a solid wall.
Bounce a medium sized ball against the wall, hard enough so that it bounces back for you to catch.
If this is difficult to do with both arms, then use your strongest arm.
Try changing where the ball hits the wall, so that you have to reach to the side to catch it.
If this seems too easy then try using a tennis ball.