FanGraphs Wins Above Replacement is considered by many in the sabermetric community be the holy grail of WAR. And, even though I’m writing a piece that is critical of fWAR, FanGraphs is still the first website I go to when I want to get a basic understanding of a specific player or team’s value. Don’t view this article as an attack on fWAR or FanGraphs, both of which I use frequently; instead, consider this article as constructive criticism.

fWAR, specifically for pitchers, is riddled with minor problems that together make the metric less valuable. In Part 1 of the series, we’re going to look at a hotly debated issue regarding fWAR that has been brought up by other readers before: the fWAR park factors.

According to the FanGraphs glossary, a basic runs park factor is used when calculating fWAR. Because FIP models ERA, using runs park factors for FIP shouldn’t be a problem.

Unfortunately, this idea simply isn’t true. The inputs of FIP, HR/9, BB/9, and K/9, only include about 30% of plate appearances. Some ballparks (Citi Field for example), inflate HR/9 and FIP despite suppressing runs in general. If Pitcher fWAR is based on FIP, FIP park factors, not runs park factors, must be used. Below is a table comparing runs and FIP park factors for different teams/ballparks, with FIP park factor equaling ((13*HRPF)+(3*BBPF)-(2*SOPF))/(14), with all of the data coming from the FanGraphs park factors.

Season Team Basic FIP Difference 2014 Reds 101 112 -11 2014 Brewers 103 111 -8 2014 White Sox 104 111 -7 2014 Yankees 103 110 -7 2014 Mets 95 102 -7 2014 Phillies 100 106 -6 2014 Dodgers 96 101 -5 2014 Orioles 102 107 -5 2014 Blue Jays 103 108 -5 2014 Astros 100 104 -4 2014 Indians 97 100 -3 2014 Padres 94 96 -2 2014 Mariners 97 97 0 2014 Rays 95 95 0 2014 Rangers 106 106 0 2014 Braves 99 99 0 2014 Diamondbacks 104 103 1 2014 Cubs 102 101 1 2014 Rockies 117 116 1 2014 Tigers 102 101 2 2014 Nationals 100 97 3 2014 Angels 95 92 3 2014 Athletics 97 93 4 2014 Cardinals 98 94 4 2014 Giants 93 88 5 2014 Royals 101 96 5 2014 Twins 101 95 6 2014 Pirates 97 89 8 2014 Red Sox 104 96 8 2014 Marlins 101 90 11

In addition, the standard difference between the Basic and FIP park factors was a staggering 5.5. Clearly, using runs park factors on FIP significantly benefits and hurts certain teams’ Pitcher fWAR.

While the Marlins, Red Sox, Pirates, Twins, and Royals benefit from park factors that overestimate their ballpark’s FIP-inflating ability, the Reds, Brewers, White Sox, Yankees and Mets experience the opposite effect, falsely increasing/decreasing these teams’ Pitcher fWAR.

Looking at the team pitching leaderboards, the effect of this mistake is pronounced on several teams’ fWAR. For example, the Mets, despite ranking 9th in the National League in FIP while playing in a ballpark that inflates FIP by 2%, rank dead last in the National League in Pitcher fWAR. Similarly, the Red Sox rank 5th in the AL in Pitcher fWAR despite ranking 10th in the AL in FIP and playing in a ballpark that suppresses FIP by 4%.

Using FIP park factors instead of runs park factors is a simple change that would vastly improve the accuracy of Pitcher fWAR. In the next segment of “Trying to Improve fWAR”, I’ll examine the league adjustments (or lack thereof) in both Position Player and Pitcher fWAR.