Teamwork is a first order concern for any organization bigger than a single individual. This paper provides a novel identification approach to measure value-added from teamwork net of solitary work. Holding constant the assigned task, compare a worker’s contribution to output when acting alone versus when working in a team. Define the discrepancy between the two as that worker’s value-added due to teamwork. The current application to professional tennis finds that one-fifth to one-third of output variation is explained by team value-added, and over one-half of across-team variation. Players match assortatively by both own skill and team skill dimensions, but do not sort interdimensionally. Additionally, a specification test statistically fails to reject the log additive production function.