During the early days of professional baseball, the dominant major leagues imposed a “reserve clause” designed to limit player wages by restricting competition for labor. Entry into the market by rival leagues challenged the incumbent monopsony cartel's ability to restrict compensation....

Past studies estimating the marginal revenue products of baseball players have assumed individual players' hitting performances to be independent of teammate spillovers. However, the baseball community's widely held belief in "protection" - that a good (bad) player can improve (diminish) the hit...