large rubber ball or nerf ball
whistle
blindfold

Divide into two teams.
Have one non-blindfolded referee right on the center line to judge points.

One team on each side of the center line.

The ball is placed on the center line.
One person is blindfolded and given the whistle.
When he blows the whistle, the game begins.
When he blows the whistle again, whichever side of the center line the ball is on receives one point - even if the ball is in the air and has not touched ground on that side.
Play resumes when he blows the whistle again.

The team with the fewest points after a set time limit wins - 5 minutes.

Mix teams after a few rounds if it is very one-sided.