Recreational sports injuries are expensive to society. Prevention of such injuries must be a major public health goal. In a previous retrospective study, base sliding was found to be responsible for 71 % of recreational softball injuries. Because most injuries occurred during rapid deceleration against stationary bases, quick-release (break-away) bases were evaluated as a means to modify this mechanism of injury. In a prospective study, 633 softball games were played on break-away base fields and 627 games were played on stationary base fields. Forty-five sliding injuries occurred on the station ary base diamonds (1 injury for every 13.9 games) and only two sliding injuries occurred on the break-away fields (1 injury for every 316.5 games). The medical costs for injuries on the stationary base fields was 79 times greater than that on the break-away fields. In a 1035 game follow-up study performed on all fields equipped with break-away bases, two sliding injuries occurred (1 injury for every 517.5 games). Installing break-away bases in fields used by recrea tional leagues would achieve a significant reduction of serious softball injuries (98%) and, therefore, should be mandatory. Based on our findings, the Centers for Disease Con trol has estimated 1.7 million injuries would be pre vented nationally per year, saving $2.0 billion per year nationally in acute medical care costs.