COR (Coefficient of Restitution)

COR is a dimensionless ratio between 0 and 1: 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 typically fall in the 0.40 to 0.55 range, with most associations using either 0.44 or 0.52 as their legal standard. A 0.52 COR ball rebounds at 52% of its pre-impact speed. This means and since this means less energy is absorbed by the ball on each bounce, more energy is available to be transferred to the ball through the bat at contact.

COR interacts directly with BPF to determine total exit velocity. A 0.52 COR ball hit by a 1.20 BPF bat generates by a lot 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. This means 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 that no amount of mechanical adjustment can close. This means the energy ceiling is set by the equipment, not the swing. Understanding this prevents misattributing poor carry to mechanics when the real cause is a regulatory equipment difference.