A FanGraphs WAR Fielding Update

4/23 Update: It has come to our attention that in the switch to Statcast Fielding Runs Prevented (RAA), outfield positional adjustments were being improperly applied. This has now been corrected by zeroing out RAA for each individual position, on a seasonal basis, specifically for use in WAR. The tables below have been updated to include this correction.

Since we launched FanGraphs WAR in 2008, we have used various components of Ultimate Zone Rating (UZR) such as Range, Outfield Arm, and Double Play Conversion to evaluate position player fielding. Today, we’re changing one of those components. Retroactive to the 2016 season, we have swapped out the Range component of UZR for the Statcast metric Fielding Runs Prevented, which is Outs Above Average (OAA) converted to runs above average. The UZR Outfield Arm and Double Play Conversion components of WAR remain unchanged.

We believe the additional data points available in Statcast, such as a fielder’s starting location, help to improve the measurement of a player’s range, especially in situations where players are shifted.

The vast majority of players’ new WAR calculations fall within a +/-1 WAR range of their previous WAR figures. Since 2016, there are 49 individual seasons that have changed by more than one win, and 14 players whose WAR has changed by more than three wins for the entire six year span starting in 2016.

On the leaderboards, we have a new custom field called “Legacy WAR (L-WAR),” which will show the results of the previous calculation for those who are interested in making comparisons.

Below is the list of players who experienced the biggest single season changes, followed by the list of the players with the largest changes since 2016.