Wins above replacement (WAR) seeks to boil down a player’s value on the field to a single number. For position players, it takes into account production at the plate, defensive metrics, and also position – certain defensive positions, such as shortstop, have a higher inherent value than others, such as first base. As for pitchers, WAR uses stats like runs given up, innings pitched, and field-independent-pitching (FIP) to calculate a pitcher’s value.
A WAR of 0 indicates an average player or a replacement-level player. Players with a WAR greater than zero are above-average players, and players with a WAR lower than zero are below-average players.