Remember many days ago when we talked about how pesky it is to have a ball in play? That’s as true for pitchers as it is for hitters. So, some enterprising folks struck out to roughly measure ERA in a way that ignores balls put in play, instead focusing entirely on the Three True Outcomes. Fielding Independent Pitching (FIP) is a defense-agnostic statistic to compare against ERA, and in some ways is an ideal “predictor” statistic for ERA.
The calculation for FIP lies somewhere between what we saw for OBP and wRAA. It weights Three True Outcome results (home runs, walks and hit by pitches, and strikeouts) differently based on their relative impact on the game historically, then we add the weighted values and adjust by a constant so that league-average FIP is exactly equal to league-average ERA.
\text{FIP} = \frac{13\times \text{HR} + 3\times(\text{BB}+\text{HBP})-2\times \text{K}}{\text{IP}} + \text{FIP Constant}The motivation behind FIP is that everything not included in the above calculation, namely balls in play, results in semi-random values for the pitcher. They don’t have control over how a ball in play is handled, and fluctuations in BABIP across seasons imply that including that data doesn’t improve the accuracy of ERA as an evaluation tool. So, FIP is independent of any defensive performance, and is generally considered a “truer” evaluation.
More importantly, comparing FIP and ERA lets us see the results of those messy plays in context. If a pitcher’s ERA is significantly lower than their FIP, they have a mix of good defense and good luck with where balls were hit. Conversely, a good FIP but bad ERA means the team’s defense let them down, and perhaps they got pretty unlucky with how balls were hit. In both cases, we generally expect ERA to regress towards FIP: a player with a lower ERA and high FIP should not be counted on as elite the following season, while a low FIP-high ERA pitcher could be a solid gamble next season.
As promised, let’s take a look at how this played out for Zack Britton. In 2016 he had a remarkable 0.54 ERA, good for an 803 ERA+. Any result this extraordinary will regress the following year, but the question is by how much?
In 2014, Zack had an ERA of 1.65 and a FIP of 3.13. Then, in 2015 he showed some solid improvement overall: His ERA was slightly worse at 1.92, but his FIP was 2.01. Clearly he made some adjustment, and these Three True Outcome results (again, often more important for a reliever) were under control. He only barely out-performed his FIP, so we can consider this a natural state.
Moving onto 2016 we see that ERA of 0.54. That is clearly an outlier, and his FIP of 1.94 indicates that he was only barely better as a pitcher than in 2015. He just had a run of luck with balls in play, where perhaps he had a few key defensive players step up, or balls in play simply didn’t find gaps. Regardless, we could safely assume his 2017 would not be a repeat, and at best his ERA would be around 2.00.
Sure enough, his ERA ballooned to 2.89 in 2017, along with an increase of FIP to 3.40.1FIP can’t predict future FIP, so our hands are tied in this case. It appears he had hit his peak in 2016, and was lucky that his athletic peak coincided with a peak in luck, resulting in some amazing statistics. Since 2016, his FIP has been below 3.00 only once, and his ERA has been below 2.00 only twice.
Using FIP is straightforward: treat it exactly like ERA with the same scaling, using it either on its own to directly compare players, or to compare it to a player’s ERA to understand their relative performance.
Let’s close out with some FIP exploration.
- Bob Gibson’s 1968 season wasn’t too much of a fluke: his FIP was still 1.77
- Funnily enough, Dwight Gooden’s 1985 season — his best by ERA — is worse than 1984 when comparing FIP. His 1.53 ERA in 1985 comes with a 2.13 FIP, while in 1984 he managed a 1.63 FIP(!) with a 2.60 ERA. Unlucky!
- The best FIP in the live ball era was Pedro Martînez’s 1.39 in 1999.2I need you to know I wrote an entire additional section about Dazzy Vance, a pitcher from 1925 who evidently had an ERA of 3.53 and, somehow, a FIP of 1.78. Turns out Baseball Reference just has that wrong, and his FIP was actually 2.69 (I calculated it by hand and confirmed it on FanGraphs.) I can’t find anywhere to report an error on this.
Continue to Day 16 – Pitcher Miscellany
- 1FIP can’t predict future FIP, so our hands are tied in this case.
- 2I need you to know I wrote an entire additional section about Dazzy Vance, a pitcher from 1925 who evidently had an ERA of 3.53 and, somehow, a FIP of 1.78. Turns out Baseball Reference just has that wrong, and his FIP was actually 2.69 (I calculated it by hand and confirmed it on FanGraphs.) I can’t find anywhere to report an error on this.