Water Ballon Battleship

This game is best played outside in the grass.

Divide everyone into 2 teams and have each team on either side of a divider that's at least 4 or 5 feet high. (The divider can be made out of sheets/tarps draped over a volleyball net. The point is that the people on one side will not be able to see the people on the other side when everyone is crouched low or lying down.)

Each person on each team is given a water balloon. They duck down low and move to a place on their side of the divider where they lie down, and have to stay.

When everyone is in position, the organizer/referee yells "Fire!" and each team lobs their water balloons over the divider with the goal of hitting someone on the other side (having no knowledge of where their opponents are positioned on the floor). Everyone who is hit is out. The remaining players get a new water balloon.

Repeat the game until everyone on one team is out.

Tip: Keep pretty small boundaries for the game; water balloon are small enough and get used quickly enough that you want there to be a fair chance of people getting hit. Also, don't let anyone lie within 6 feet of the divider in the middle -- it's too hard for people to throw a balloon so that it makes it over the divider and lands close to it on the other side. People in that area would almost certainly not get hit, and where's the fun in that?

Make sure everyone knows they will probably get wet playing, so they can dress accordingly.

Supplies:
filled water balloons
volleyball setup (poles and rope, anyway)
sheets or tarps