What are FIP and xFIP? Sabermetrics Glossary for Fantasy Baseball (2025)

February 11, 2025

What are FIP and xFIP? Definition and meaning of FIP (Fielding Independent Pitching) and xFIP (expected Fielding Independent Pitching) as part of our sabermetrics glossary for fantasy baseball.

Welcome RotoBallers to our overview of FIP (Fielding Independent Pitching) and xFIP (expected Fielding Independent Pitching). This article is a deeper dive into FIP/xFIP and is part of our ongoing series "Using Sabermetrics for Fantasy Baseball."

In this article, we'll explore how to separate a pitcher's performance from his supporting cast and luck using metrics on the same scale as the familiar earned run average (ERA). We'll also look at how FIP and xFIP foreshadow regression and two types of hurlers who may consistently "beat" their peripherals in layman's terms.

You can find our entire sabermetrics glossary, which includes links to many other sabermetric stats as part of this series. Each stat deep dive will be released over the next few days. Stay tuned!

What Are FIP and xFIP? Sabermetrics Glossary

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 teammates.

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 determining 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 assumes league-average homers based on fly balls allowed. Some pitchers are consistently more or less homer-prone than average, but studies show that xFIP is a more reliable ERA predictor than 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 the league average FIP, xFIP, and ERA are identical (4.08 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!

How to Use FIP and xFIP

This predictive nature of FIP and xFIP is why 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 is 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 time.

For example, Ronel Blanco surprised many with a 2.80 ERA over 167 1/3 innings for the Astros last season. Sadly, Blanco's 4.15 FIP and 4.09 xFIP strongly suggest he isn't that good. Fantasy managers expecting a repeat are likely to be disappointed.

Certain types of pitchers may consistently defy FIP. The first is knuckleball guys, who have challenged DIPS theory since its introduction.

Matt Waldron is the only knuckleballer right now, and his 4.35 ERA was better than his 5.46 FIP and 4.79 xFIP in 2023. The trend continued during his strong first half in 2024, as he logged a 3.71 ERA against a 3.88 FIP and 4.39 xFIP over 106 2/3 IP. The explanation is that effective knuckleballers induce weak contact as a sustainable skill, like Bobby Witt Jr.'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:                                                                                                                              ERA                       FIP                        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. Those banking on a return to form were disappointed in 2022. Hendricks recovered somewhat in 2023, but he was dreadful last year.

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.

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. Nick Lodolo posted a 4.76 ERA for the Reds last year, but his SIERA was 3.78, partly to "correct" for Great American. Pitching in Cincinnati will not improve your ERA, so you can't count on Lodolo regressing to his SIERA, given his home park.

SIERA isn't on the ERA scale either, with a league average of 3.99 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, Blanco fares slightly better with a 4.00 mark, Hendricks has a 4.81 figure that splits the difference between his FIP and xFIP, and Lodolo's 3.72 suggests upside despite his hostile park.

Conclusion

To conclude, FIP and xFIP are metrics that try to determine the ERA a pitcher deserves based only on the outcomes he controls: Ks, BBs, and HR 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 more accurately than ERA alone. xERA is a useful metric for the Statcast-inclined.

Stay tuned to learn more about how analytics can help you prepare for 2025 fantasy baseball drafts.

More Sabermetrics & Statcast for Fantasy Baseball