Rocks can be targets. So can boxes, toy cars, piles of leaves and old sweatshirts. Make the scoring system equal to the task. Each target is worth a certain kind of hit. Easy targets are singles, harder ones are doubles and so on.
Players take turns throwing at the targets.
If the target is hit, the player's team gets the corresponding award. If the target is missed, that player's team is given one out. When the thrower has three outs, the next thrower comes to bat. Play as many innings as you like, keeping score. The player with the most hits gets to pick the next targets.