Wins above replacement

Wins Above Replacement or Wins Above Replacement Player, commonly abbreviated to WAR or WARP, is a non-standardized sabermetric baseball statistic developed to sum up "a player's total contributions to his team". A player's WAR value is claimed to be the number of additional wins his team has achieved above the number of expected team wins if that player were substituted by a replacement-level player: a player that may be added to the team for minimal cost and effort.

Individual WAR values are calculated from the number and success rate of on-field actions by a player (in batting, baserunning, fielding, and pitching), with higher values reflecting larger contributions to a team's success. WAR value also depends on what position a player plays, with more value going to weaker hitting positions like catcher than positions with strong hitting such as first base. A high WAR value built up by a player reflects successful performance, a large quantity of playing time, or both combined.

For example, Fangraphs rates Clayton Kershaw's 2014 regular season performance at 7.2 WAR, suggesting his team won roughly seven more games than would be expected if his innings were pitched by a replacement level player. Kershaw achieved this high WAR total by pitching many innings while maintaining a high rate of strikeouts and low rates of home runs and walks.

The basis for a WAR value is the estimated number of runs contributed by a player through offensive actions such as batting and baserunning, and runs denied to opposition teams by the player through defensive actions like fielding and pitching. Statistics such as weighted on-base average (wOBA), ultimate zone rating (UZR), ultimate base running (UBR), and fielding-independent pitching (FIP) measure the effectiveness of a player at creating and saving runs for their team, on a per-plate appearance or per-inning basis. These statistics can be multiplied by the playing time of a player to give an estimate of the number of offensive and defensive runs contributed to their team.

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