FIP/xFIP: Using Sabermetrics for 2024 Fantasy Baseball

Rick Lucks breaks down how to use FIP and xFIP to identify pitching sleepers and busts as his 2024 series on making sabermetrics more accessible for fantasy baseball managers continues.

While we've only examined how to evaluate hitters using advanced stats thus far, sabermetrics are just as useful for pitchers. The first advanced pitching stat most fantasy managers encounter is Fielding Independent Pitching or FIP. FIP measures a pitcher's actual skill instead of the effects of luck or his supporting cast. According to DIPS (Defense Independent Pitching Statistics) theory, pitchers control only Ks, BBs, and home runs allowed. Therefore, Ks, walks, and dingers are the only inputs to determine FIP.

Sometimes xFIP is cited instead of FIP. The "x" stands for expected and acknowledges that HR/FB is just as variable for pitchers as hitters. While FIP uses a player's actual homers allowed, xFIP charges him with a league-average amount of homers based on his fly balls allowed. Some pitchers are consistently more or less homer-prone than average, but studies show xFIP is a more reliable predictor of future ERA than regular FIP.

For fantasy purposes, it's sufficient to understand the three primary inputs listed above and that both stats are on the ERA scale. That means that if a FIP or xFIP would be a good ERA, it is a strong number. The math is perfect, meaning that the league average FIP, xFIP, and ERA are identical (4.33 last year). FIP and xFIP are displayed on the right-hand side of the first table for pitcher pages on FanGraphs, so they're very accessible. Let's get started!

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How to Use FIP and xFIP

This predictive nature of FIP and xFIP is the reason fantasy managers should care about them. Both metrics predict future ERA more reliably than ERA itself, making them a good go-to stat to determine if an early breakout may be for real or if a struggling superstar is likely to rebound. All things being equal, it is generally expected that a pitcher's ERA will regress toward his current FIP and xFIP over a season or across seasons.

For example, Blake Snell earned the NL Cy Young Award by posting a 2.25 ERA over 180 IP in 2023, but his 3.44 FIP and 3.62 xFIP suggest his ERA should have been more than a full run higher. The shiny ERA masked career worsts in BB% (13.3) and Zone% (32.6), and fantasy managers who draft him expecting a straight repeat are likely to be disappointed. Julio Urias was last year's example, and his ERA ballooned to 4.60 before domestic violence allegations ended his season early.

Certain types of pitchers may consistently defy FIP. The first is knuckleball guys, who have challenged DIPS theory since its introduction. Matt Waldron was the only knuckleballer in 2023, and his 4.35 ERA was better than his 5.46 FIP and 4.79 xFIP. The explanation for this is that effective knuckleballers induce weak contact as a sustainable skill like Julio Rodriguez's legs or Luis Arraez's liner prowess.

The other type is simply called a "FIP-beater" that manages to control contact against him to the point that he outperforms his peripheral stats. Kyle Hendricks had an amazing stretch of doing this from 2016-2020. In 2016, his 2.13 ERA was backed by just a 3.20 FIP and 3.59 xFIP. In 2017, his 3.03 ERA was backed by a 3.88 FIP and 3.76 xFIP.  In 2018, a 3.44 ERA was backed by a 3.78 FIP and 3.87 xFIP. 2019 saw a 3.46 ERA with a 3.61 FIP and 4.26 xFIP, and the shortened 2020 season saw a 2.88 ERA with a 3.55 FIP and 3.78 xFIP.

Using sabermetrics, you would have expected significant regression in each of these years only to be proven wrong. However, his ERA was consistently trending upward outside of the COVID season. The house of cards came crashing down in 2021 when Hendricks posted a 4.77 ERA against uninspiring FIP (4.89) and xFIP (4.61) marks. Those banking on a return to form were disappointed in 2022 as Hendricks posted a 4.80 ERA backed by a 4.82 FIP and 4.46 xFIP.

Hendricks recovered somewhat last year with a 3.74 ERA, 3.81 FIP, and 4.13 xFIP, but why roll the dice? Pitchers like this rarely make good fantasy investments. Strikeouts are a key component of FIP, so pitchers who defy it are often lacking in a common fantasy category even if they post strong ratios. There is an ongoing debate though, so this author's word isn't gospel on the subject.

What Are SIERA and xERA?

SIERA stands for Skill-Interactive ERA and attempts to measure a pitcher's true talent more accurately than FIP or xFIP. It's marginally more accurate than xFIP, but its increased complexity may not be worth it. The stat assumes that ground ball pitchers will have a lower BABIP on grounders than other pitchers, while fly ball pitchers will have lower HR/FB marks. It's also adjusted for the overall run-scoring environment and a pitcher's home park.

That may sound good, but remember that those adjustments won't affect your fantasy team's bottom line. Hunter Greene posted a 4.82 ERA for the Reds last year, but his SIERA was 3.74 partly to "correct" for Great American. Pitching in Cincinnati will not improve your ERA, so you can't count on Greene regressing to his SIERA given his home park. SIERA isn't on the ERA scale either, with a league average of 4.24 last season.

A Statcast metric called xERA (Expected ERA) is SIERA but better, incorporating Statcast contact quality metrics such as average launch angle instead of SIERA's broad assumptions. It's also on the ERA scale. Using xERA, Snell fares even worse with a 3.77 mark, Waldron gets credit for the weak contact he induced with a 4.42, Hendricks has a 4.18 figure that splits the difference between his FIP and xFIP, and Greene's goes up to 3.82 to acknowledge the realities of pitching for the Reds.

Conclusion

To conclude, FIP and xFIP are metrics that try to determine the ERA a given pitcher deserves based only on the outcomes he controls: Ks, BBs, and home runs allowed. While FIP uses the pitcher's actual homers allowed, xFIP regresses it to the league average. Both metrics are on the ERA scale and may be used to predict future ERA with more accuracy than ERA alone. Meanwhile, xERA is a useful metric for the Statcast-inclined. Stay tuned to learn more about how analytics can help you prepare for 2024 fantasy baseball drafts.