The Amateur Softball Association governs the rules and regulations of sanctioned softball leagues. The ball size used in ASA games depends upon the game being played, and the age and sex of the players. Men's softball leagues use 11-inch balls which, along with their smaller size, take more force to compress. This results in a faster, and farther-flying ball. Women's and youth leagues typically use the 12-inch ball. The larger 12-inch ball compacts easier and slows the game down relative to the 11-inch ball.
National Collegiate Athletic Association
The National Collegiate Athletic Association protects collegiate student athletes by governing intercollegiate sports. They advocate fair, safe, equitable and sportsmanlike intercollegiate competition. The NCAA 2010 and 2011 "Rules and Interpretations" state that the regulation-sized softball must measure between 11 and 7/8 inches and 12 and 1/4 inches, with a weight of at least 6 and 1/2 ounces, and not to exceed 7 ounces. They also specify the compression and "dynamic stiffness" of a regulation ball. The NCAA women's softball league is a fast-pitch league.
Men's softball leagues and fast-pitch softball leagues typically use 11-inch softballs. Youth leagues and women's leagues typically use 12-inch softballs. In intercollegiate sports, women's fast-pitch softball also uses the 12-inch ball. However, amateur women's fast-pitch softball leagues may use either the 11-inch or 12-inch softball. The size of the ball used depends on the league rules and regulations. The most significant difference between the 12- and 11-inch softball is the speed of the game.
Backyard and Saturday Afternoon Softball
When playing a pickup game in the community park or the backyard, you may play with whatever sized softball you can find. When planning a game outside of league play, keep in mind the age of the players when choosing the ball. The larger ball provides a larger and slower target for the players to throw, hit and catch. The most important aspect of playing pickup softball is not whether the ball is 11 or 12 inches, it is whether the players are having fun.