Divide your group into two teams (Team A & Team B). You may be able to use more groups. We had about 5-6 per team, and that worked pretty well.
One person from Team A stands with his back to the two groups (about 10-15 yards away seemed right) and someone from Team B tries to hit him with a dodge ball or some other type of ball. If he hits him, then the Team A person joins Team B. If not, he stays with Team A.
Next the thrower takes his place as the person being thrown at, and the next person from Team B throws at him.
Keep going until everyone has moved to one team. We put the person being thrown at against the side of the shed, and that helped so we didn’t have to chase the ball all the time.
We live in Lancaster County, PA where the Amish are, so we called this “Dutchie Dodgeball”! 🙂