Knuppelprestatiefactor (BPF)

BPF is calculated by comparing the ball's rebound speed off the bat barrel to its rebound speed off a completely rigid surface. Both are measured at the same impact speed. A bat with a BPF of 1.20 sends the ball back 20% faster than a rigid wall would at the same impact speed. That extra energy comes from the barrel's elastic deformation at impact (the "trampoline effect"). The barrel compresses slightly under force and springs back, adding velocity to the departing ball. The key insight is that BPF captures performance the bat adds on top of what pure bat speed provides. It is the equipment's contribution, not the hitter's.

Associations cap BPF to keep games safe and competitive. USSSA caps its slow-pitch bats at 1.20 BPF. USA Softball does not use BPF; it certifies bats against a batted-ball speed limit of about 98 mph. A bat that exceeds the legal limit is not merely a performance advantage. It is grounds for forfeit of games in which it was used. Some associations maintain banned bat lists, updated seasonally as manufacturers push the limits. BPF certification is usually stamped on the bat rather than tested at the park. So knowing your association's approved-bat list is the only reliable way to confirm legality.

BPF and COR are sometimes confused. COR describes the ball's elasticity; BPF describes the bat barrel's elasticity. Both are regulated because together they determine total energy transfer at contact. A high-BPF bat paired with a high-COR ball produces maximum exit velocity — which is precisely the combination associations are designed to cap. In practice, a hitter using a legal 1.20 BPF bat with a sanctioned ball is already near the performance ceiling the equipment rules allow. The remaining variable is swing mechanics.