Equipment needed: a base for every 3 players and a ball for every 5.
Spread bases throughout the desired play area, with approximately one base for every three players. Have a player with a foam ball (an It) for every five players. If you are not It and are hit with the ball, you become It and take the ball to hit someone else who is not It. If you are on a base, you are safe and cannot be hit (and if you are hit, you are still not it). However, if someone comes up and wants the base, you must move and cannot immediately return to the same base.
Remind players to be alert so they can avoid crashes.