You'll need a few friends to form teams, and a net or obstacle to use as a net.
Each team needs a bed sheet, and a good supply of water filled balloons.
Each team member holds a corner or side of the sheet. Put a water balloon on the sheet. Using lots of teamwork, bounce the balloon on the sheet until you can flip it over the net.
The other team must catch it in their sheet and flip it back.
For smaller groups or young children, use a smaller sheet or a tablecloth.
You can also use a ping- pong ball instead of water balloons.