Baseball has terrific and comprehensive performance data to which it pays assiduous attention, and an outcomes-based culture. Yet its collective agreement forbids pay-for-performance (P4P) based on players' reaching certain statistical performance targets, like number of home runs or stolen bases. Health care ignores far more data than it pays attention to, yet P4P has been touted in many organizations as the solution to problems of quality and efficiency. This despite the dearth of comprehensive, valid data that relate what a provider does to how well her patients do. This post explains what baseball understands about P4P and why what seems to be a good idea in theory is fraught with unintended consequences in practice.