COR (Coefficient of Restitution)

COR is a dimensionless ratio, a pure number with no units, between 0 and 1. It equals the rebound speed of the ball off a rigid surface divided by its impact speed. A perfectly elastic collision would yield a COR of 1.0 (all energy returned). A perfectly inelastic collision yields 0 (all energy absorbed). Softballs used in regulated play usually fall in the 0.40 to 0.55 range. Most associations use either 0.44 or 0.52 as their legal standard. A 0.52 COR ball rebounds at 52% of its pre-impact speed. That means less energy is absorbed by the ball on each bounce. So more energy is available to be transferred to the ball through the bat at contact.

COR interacts directly with BPF (Bat Performance Factor) to determine total exit velocity. Take a 0.52 COR ball hit by a 1.20 BPF bat. It generates significantly more exit velocity than the same bat with a 0.44 COR ball, or the same ball with a lower-BPF bat. This multiplicative interaction is why associations specify both the ball and bat performance limits together. Controlling only one allows the other to compensate and produce the same outcome. It is also why cross-association equipment violations often involve mismatched COR and BPF combinations rather than either one being wildly over-spec in isolation.

For hitters, COR translates into the feel of contact and the practical distance ceiling. A high-COR ball at full compression feels crisp and springs off the barrel with an audible resonance. A lower-COR ball feels softer and produces less carry on the same hit. Hitters who move between associations with different COR standards will notice distance differences. No amount of mechanical adjustment can close them, because the energy ceiling is set by the equipment, not the swing. Understanding this prevents blaming poor carry on mechanics when the real cause is a regulatory equipment difference.