Effective on January 1, 2018, Little League Baseball® will adhere to the new USABat standard. No bats previously approved for use in Little League Play (Junior League Baseball and below) will be permitted to be used in any Little League game or practice, or other Little League function, event, or activity. For more information on the USABat standard and a complete list of bats approved through the USABat Standard, visit usabat.com.  

Little League FAQ for new bat standards. http://www.littleleague.org/learn/equipment/baseballbatinfo/USA-Baseball-Bat-Standard-FAQs.htm