BESR, or Ball Exit Speed Ratio, is a rule that applies to all nonwood bats used by all teams affiliated with the NCAA and by all high schools who are members of the National Federation High School Associations (NFHS). All nonwood bats used must bear the BESR certification mark. The BESR certification process, which has been conducted at the Baseball Research Center at UMass-Lowell Department of Mechanical Engineering, ensures a nonwood bat meets four criteria: 1. The maximum exit speed is similar to the performance of the best northern white ash wood bat – 97 mph. 2. The bat’s length to weight differential is no greater than minus-3 (for instance a 34-inch bat must weigh 31 ounces). 3. The barrel diameter may not exceed a maximum of 2 5/8 inches, while bats in the past were 2 3/4 inches, thus the barrel is smaller. 4. The balance point of the bat meets the moment-of-inertia requirement.