Quidditch was a fictional sport where wizards would fly on broom sticks in the wizarding world of Harry Potter. This fictional game is fictional no more. Potter fans all over the world have turned this game into a phenomenon with rules and regulations and even a world cup!
There are multiple types of balls that are used in this sport as well as regulations for their size and use. Here is the rules for the different balls according to the US Quidditch Rulebook:
2.3. GAME BALLS
2.3.1. The Quaffle (see 1.2.1. Quaffle overview)
126.96.36.199. Quaffle regulations—A quaffle must be:
A. A spherical ball made of a flexible, smooth leather or leather-like cover of 12 or more panels with a separate bladder (such as a volleyball).
B. Not less than 65 cm (25.6″) or more than 67 cm (26.4″) in circumference.
C. The quaffle must maintain its spherical shape and must be neither inflated all the way nor flat so that a player could grip a bulk of the leather in one hand.
D. All quaffles used in a game must have the same characteristics regarding circumference, weight, and inside pressure.
2.3.2. Bludgers (see 1.2.2 Bludger overview)
188.8.131.52. Bludger regulations—The three bludgers must be:
A. Spherical balls made of flexible rubber-like covers (such as dodgeballs).USQ RULEBOOK 30
B. 8.5″ (21.6 cm) in diameter.
C. The bludger must maintain its spherical shape and must be neither inflated all the way nor so flat that a player could grip a bulk of the rubber in one hand.
D. All bludgers used in a game must have the same characteristics regarding circumference, weight, and inside pressure.
2.3.3. The Snitch (see 1.2.3 Snitch overview)
184.108.40.206. Snitch regulations—The snitch must be:
A. A spherical ball made of a uniform surface consisting of a fabric cover (such as a tennis ball).
B. 21 cm (8.5″) in circumference.
C. Held within a sock.
i. The sock must have a visible and unobstructed length
of 10″-14″ (30-35 cm).
ii. The sock may be tied in a knot or knots, but not to the
point that the exposed length is less than 10”.
D. The sock containing the snitch must be tucked in or attached to the shorts of the snitch runner in a manner that is secure, while allowing for the removal of the sock by the seeker.
US Quidditch Rulebook – http://www.usquidditch.org/files/USQ_Rulebook_8.pdf
Photo – http://www.bu.edu/today/2012/warm-up-at-winterfest/