For participants to throw the ball over the covered net and hope the other team doesn't catch it.

Divide the participants in two equal teams.
Have them go on opposite sides of the net.
Put the blanket, parachute, tarp etc. over the net or on one side, so that the teams cannot see each other.

1. Give one ball to one team and another to the other team.
2. At anytime participants can throw their ball over the net in hopes that the other team won't catch it.
3. The net being blocks provides the element of surprise.
4. Participants can pass the ball to each other on their side and strategize on when and where to throw the ball.
5. If a team throws the ball over the net and no one on the other side catches it, then the team that threw it gets a point.
6. The leader needs to be able to see both sides so that they can be the referee and judge.
7. Play until a team gets a set amount of points or for a set amount of time.

Throw in more balls as the game goes on.
If a participant attempts to catch a ball and misses, they are eliminated and have to sit out for the remainder of the game. Or they have to sit down where they missed the ball, and cannot stand up unless they catch a ball where they're sitting.
Use beach balls for younger participants.

Adaptations (General):
Encourage team members to involve all participants.

Adaptations (Blindness/Visual Impairment):
Use a ball with a bell inside, or with a plastic bag tied around it, so that participants who are blind or visually impaired can hear it.