This new BBCOR standard measures bat performance and replaces the previous BESR standard. The NCAA (college) began requiring BBCOR starting with the 2011 season. For NFHS (high school) play, all bats must be BBCOR certified for the 2012 season and beyond. BESR (Ball Exit Speed Ratio) is no longer considered accurate enough to determine the actual performance of differing bat models.
Instead of measuring the speed of the ball after it is batted, BBCOR measures the “bounciness” of the ball and bat, or the “trampoline” effect. When a bat hits a ball, the ball actually compresses / deforms by nearly a third at high pitch velocities.