There are two baseball bat rules that were put into effect for the 2013 season and beyond that affect players at the Midget, Junior, and Senior levels:

 
   1.)  Any bat that is a "-3" bat (for example, a 32"/29oz) must be a BBCOR-certified bat.
 
  2.)  All other bats -- that is, any bat that is not a -3 (for example, a 28"/18oz or a 32"/27oz) -- must have the
        USSSA BPF 1.15 certification.
 

For both certifications, the bat will have a stamp or logo clearly visible on it. Umpires will be checking bats for the certification stamp.

-3 bats are somewhat rare for JBO players, used mostly by stronger senior-level players. -3 BBCOR bats are required for high school play, so a -3 bat purchased for JBO play will be usable in high school.

Most bats purchased since 2011 will have the right certifications, but it's important to check on this before beginning game play.

Rule #1 was added for 2012.
Rule #2 was added for 2013.
 
These rules does not apply to T-Ball, Rookie, or Midget International leagues. All bats are legal for those leagues.