Smash factor is ball speed divided by club speed, a TrackMan metric that describes how efficiently club speed is converted into ball speed. A driver smash factor near 1.50 is an excellent benchmark; for example, 100 mph of club speed with a 1.50 smash factor produces about 150 mph of ball speed. The USGA and R&A regulate club head spring effect through equipment-conformance tests rather than by setting a smash-factor limit.