[waltjp]

Ball rotation depends on a number of factors. First of all check to see what your local customs are. Here in NJ it's not customary to change balls on every play as it is in other areas.

Another factor is the competency of your ball boys. It is not the job of the officials to search the sidelines for new balls. If a team wants/expects a new ball to be put in the game they had better make sure it's ready and available.

Weather - if it's wet we'll change balls on each play. Make sure the ball boy has an assistant - one to hold the balls and one to dry the balls.

Long incomplete passes. Good time to change balls if it helps to keep the game moving. Again, the ball boy must be ready for a new ball or you may end up spending more time searching for him on the sideline than it would take to retrieve the original ball.