Use two large jumpropes to create a circle in the grass. Place 10 to 20 playground balls in the center of the circle. Have all the kids stand about 10 feet outside of the circle and take turns rolling a large basketball into the circle, trying to knock the playground balls out of the circle without the basketball following suit. If a player succeeds, she gets to keep the balls she knocked out and rolls again. When all of the balls have been knocked out of the circle, the player who collected the most balls wins the game.