Call team 1 up to the front of the room. The batter gets a question or math fact to answer. If he gets it right, he moves to 1st base. If he misses it, that is an out. I usually play 5 outs so we don't have to change teams as often.
Students chalk up their runs on the board as they come in.
The other team sits in their seats and holds up fingers to show the number of outs. This game was the class favorite, and we always played it at recess on rainy days. Another rainy day favorite is Heads Up, but the kids always peek to see who tapped them, so I've changed the rules a bit. Select 7 players to come up front. Each child taps someone and then goes back up front.