Take a volleyball. Shrink it down and tie a patch of its net to a trampoline frame. No, not a big trampoline that your mama says will crack your skull open if you fall off, one of those little round ones people use to work out. Now find 3 other athletic, or at least semi-coordinated people, preferably trash talkers who have had too much Red Bull, and split into 2 teams. There. You're ready to play Spikeball.
Another Shark Tank darling, Spikeball is a 2-on-2 game for the back yard, the beach, or even the shallow water if you're willing to hack up a noodle and glue it to the Spikeball frame's legs so your net will float. Rules are similar to volleyball in that each team is allowed up to 3 midair hits between them before a spike-down transfer to the other team is required. Teams score when opponents miss the ball ricocheting of the net, or flub it up during their 3 touches. Winning score is 21.
The pictured Spikeball set is the company's Combo Meal, which includes the net, 3 Spikeballs, instructions for play, and a backpack with interior pocket for small personal items.