When your new bat is delivered to you, probably one of the first things you do is inspect it. In this process of looking over your bat you probably notice some anachronisms like ASA, USSSA, ISA, NSA and ISF. These are letters identifying the governing bodies that certify that this bat is acceptable for play in a given league or tournament sanctioned by the association. There are roughly 20 governing bodies in softball which maybe easily recognizable. There are however, five which we might consider as the major bodies. These five are the: Amateur Softball Association (ASA), United States Specialty Sports Association (USSSA), Independent Softball Association (ISA), the National Softball Association (NSA), and the International Softball Federation (ISF). Even though these governing bodies may follow similar guidelines and rules each governing body is separate from the others. Therefore, you must adhere to that specific governing body pending your league or tournament play. One can begin appreciate the complexity of the governing bodies relationships. No matter what governing body one might play under there are more similarities than differences. Every organization has a set of rules which promote consistent, fair, and safe play. One of the most interesting differences is in the certification of bats.
USSSA and NSA also test bats for certification. Those associations use a test developed by Dr. Brant a physics professor at New York University. This test, as attested by many players, allows for greater ball acceleration off the bat. On the field we might say these bats have more pop. Some people, possible erroneously, have referred to these bats as 100 + mph bats.
To get more detailed information on the certification procedures one can access the individual governing bodies' web sites or contact them directly. At these sites you can also find information on bats that are certified and those that are not approved for play in a particular association.