However, a 6.4 WAR player and a 4.1 WAR player are different enough that you can have a high level of confidence that the first player has been more valuable to their team over the given season.
For position players, the largest point of contention comes in measuring defense and estimating the positional adjustment. Our measures of both are more uncertain than our measures of offense, so players who get a good amount of their value through their defensive ratings likely have more uncertainty around their WAR value than players who have defensive value closer to average. This does not mean that WAR is wrong or biased, but rather that it is not yet capable of perfect accuracy and should be used as such.
For pitchers, the biggest open question is how much credit a pitcher should receive for the result of a ball in play. At FanGraphs, we use FIP which assumes average results on batted balls. We know that there is some skill involved in suppressing hits on balls in play, but we have no idea exactly how much. Therefore, WAR will sell short players with certain FIP-beating skills and oversell those pitchers whose results fall short of their FIP for reasons within their control. At this point, we don’t have a good way of assigning credit more accurately for balls in play.
However, we also house RA9-WAR, which is WAR based on runs allowed instead of FIP. This allows you to use one to inform the other however you like.
Using WAR properly is difficult because it requires you to think more abstractly than some other aspects of life. The exact number is not as important as the basic range, but this isn’t just true of WAR. This is the case with all statistics in all parts of the game.
Context:
League-average WAR rates vary. An average full-time position player is worth about 2 WAR, while average bench players contribute much less (typically between 0 and 1 WAR). Average starting pitchers also are worth around 2 WAR, while relief pitchers are considered superb if they crack +1 WAR.
For position players and starting pitchers, here is a good rule-of-thumb chart:
Scrub 0-1 WAR
Role Player 1-2 WAR
Solid Starter 2-3 WAR
Good Player 3-4 WAR
All-Star 4-5 WAR
Superstar 5-6 WAR
MVP 6+ WAR
Also, here’s a fun breakdown of all the players in baseball in 2010, courtesy of Justin Bopp from Beyond the Boxscore.
Things to Remember:
● Because there is no UZR data for catchers, the fielding component for catcher fWAR is calculated using two parts: the Stolen Base Runs Saved (rSB) metric from the Fielding Bible, and Runs saved from Passed Pitches (RPP). This accounts for a large portion of a catcher’s value, although pitch framing is not yet included in WAR. For this reason, catcher WAR is probably the least precise of all of the positions.
● WAR is context, league, and park neutral. This means you can use WAR to compare players between years, leagues, and teams.
● It is possible to have a negative WAR. In fact, the worst fWAR any player has had since 2002 is Neifi Perez from the Royals, who posted an incredible -3.1 wins in 2002.
● WAR is an estimate. You should not use WAR with the expectation that it is precise to the decimal point.
● FanGraphs’ WAR for pitchers is based on FIP (plus infield fly balls). We also have a version called RA9-WAR which is based on runs allowed. Baseball-Reference uses runs allowed and attempts to correct for the team defense.
● WAR for relievers includes a leverage component.
● There are currently 1,000 WAR per season based on a replacement level of a .294 winning percentage. Of those 1,000, 570 WAR are allocated to position players and 430 WAR are allocated to pitchers. You can learn more about the split here.
