In football, soccer and basketball, player quality has one obvious and inescapable metric: scoring touch-downs, goals, points. In baseball, it’s more complicated—it isn’t easy to directly associate a single player’s play with team wins. This is why “wins above replacement player” (WARP) has become so popular: It’s a statistic that manages to aggregate a player’s total contribution to their team—offense and defense and primary position—into one easily understood figure.