Law 2: The Ball
Not too much here other than the 5 “qualities and measurements,” which will vary depending on the age level of the players. The key thing here, as with most of AYSO refereeing, is player safety–that the ball is safe to play with. Just so long as you check to make sure you are playing with the correct ball for that particular age division (#3, #4, or #5), the air pressure is adequate, and that the ball is safe to play with (no scuffs, tears, rips in the material, etc.) you will be fine. The pressure should be such that with a firm pressure applied with your thumbs to one of the panels of the ball that it is only depressed about 1/4 inch.
AYSO uses three different sized balls in the different age divisions as mentioned above. The younger players 5U-8U use #3, 9U-12U use #4, and above that the game is played with a regulation sized #5 ball. Remember to double check what size balls you are using. Unfortunately the “#” is usually inconveniently small and hard to find/see for those of us visually impaired older stewards of the game.
For most Region 20 AYSO games, it is up to the “Home Team” to provide three balls for the match. When you are checking the Home team in before the game, make sure you remind the Head Coach that you need three of his/her good balls, properly inflated. As the CR you are responsible to check and approve the air pressure (using your thumbs; a pressure gauge is usually not necessary unless you have a finicky coach). Have one ball placed beside each goal and use the third to start the game.
Sometimes it becomes necessary during the match to change balls, for instance if a ball loses pressure during the game or if the surface of the ball becomes inadequate. In that case simply switching balls once it goes out of play is sufficient. If you find yourself having to “stop play” because players (or coaches) are informing you that the ball is no good, you will need to restart with a Dropped Ball where the defective ball was when you stopped play.
There are other more specific scenarios for when a ball “becomes defective” at certain restarts, or during a PK/KFTPM as the ball is moving forward, and how to restart play in those situations. In reality, occasions when the ball “becomes defective” during/upon taking a free kick, or when it bounces off of the crossbar, are rare (it’s never happened to me or any of my fellow referees). These scenarios don’t happen often, but just in case you might want to review what to do in the main text of The Laws Of The Game, Law 2 (pp.44).