Spikeball is one of my favorite games to play in the summer, and I'm really wishing it was warm enough to play right now! Spikeball is a game involving a hula-hoop sized net placed on the ground and 2 teams of two go back and forth hitting a small ball across it. It can be played anywhere, including the beach, the grass, maybe even the snow if you're willing to get cold! Much like volleyball, each team has 3 alternating touches to hit the ball on the net for the next team to then play. However, there are no distinct "sides" each team is allowed on, and once the ball is served, there are no boundaries to where you can move. In order to score a point, the opposing team has to make a mistake by hitting the rim, missing the net, using more than 3 touches, causing the ball to bounce more than once on the net, or letting the ball hit the ground.
Now, for the physics involved, each person must add an applied force to the ball in order for it to bounce across the net. There is much trial and error involved at first to see how much or how little force you need in order to score a point, depending on the position of the other team. Once the ball hits the net, an equal and opposite force is applied, causing the ball to bounce back up. However, this depends on how tight or how loose the net is, much like a spring constant. The tighter the net, the greater the force the ball will bounce back with; the looser the net, the less force the ball will bounce back with. The force also depends on the mass of the ball; therefore, the more air that is pumped into the ball, the greater the force the ball bounces back with.
Check out this awesome video of spikeball in action: