Table of Contents
What Is FIP?
Fielding Independent Pitching (FIP) is an advanced baseball statistic that estimates a pitcher's run prevention ability independent of the defensive quality behind them. Developed by sabermetrician Tom Tango, FIP focuses exclusively on the three outcomes that a pitcher can control without fielder involvement: strikeouts, walks (plus hit batsmen), and home runs allowed.
Traditional ERA (Earned Run Average) is influenced by the quality of a pitcher's defense. A pitcher with excellent fielders behind him will tend to have a lower ERA than an equally skilled pitcher with poor fielders. FIP strips away this defensive influence to provide a purer measure of pitching skill. Over large samples, FIP is a better predictor of future ERA than ERA itself, making it invaluable for player evaluation.
FIP is designed to be on the same scale as ERA for easy comparison. A pitcher with a 3.20 FIP is performing at roughly the same level as a pitcher with a 3.20 ERA would be expected to, controlling for defense and luck on balls in play. When a pitcher's ERA is significantly lower than their FIP, they may be benefiting from good defense or luck; when ERA is higher, they may be suffering from poor defense or bad luck.
FIP Formula Explained
The coefficients (13, 3, and 2) represent the relative run values of each event. Home runs are weighted most heavily at 13 because each home run guarantees at least one run. Walks and hit-by-pitches receive a weight of 3 as they put runners on base. Strikeouts receive a negative weight of 2 because they remove baserunners and scoring opportunities. The constant is adjusted each season to align the league-average FIP with the league-average ERA.
FIP Rating Scale
| FIP Range | Rating | Description |
|---|---|---|
| Under 2.90 | Excellent | Cy Young-caliber performance |
| 2.90 - 3.20 | Great | Top-tier starter, all-star level |
| 3.20 - 3.50 | Above Average | Solid number-two starter |
| 3.50 - 3.80 | Average | Mid-rotation starter |
| 3.80 - 4.20 | Below Average | Back-end starter, long reliever |
| 4.20 - 4.60 | Poor | Replacement-level pitcher |
| Over 4.60 | Very Poor | Below replacement level |
The FIP Constant
The FIP constant is recalculated each season and varies by league. It is determined by the formula:
The constant typically ranges between 3.00 and 3.20 in modern MLB seasons. For quick calculations, 3.10 is a reasonable approximation. The constant ensures that league-average FIP equals league-average ERA, making FIP interpretable on the familiar ERA scale.
- 2023 MLB FIP constant: approximately 3.107
- 2022 MLB FIP constant: approximately 3.078
- 2021 MLB FIP constant: approximately 3.112
- Historical range: 2.90 to 3.30
Frequently Asked Questions
Why is FIP better than ERA for evaluating pitchers?
ERA is heavily influenced by factors outside a pitcher's control, including defensive quality, ballpark effects, and sequencing luck. FIP isolates the outcomes that pitchers directly control. Research shows that FIP predicts future ERA more accurately than past ERA itself, especially over smaller sample sizes like a single season.
What is the difference between FIP and xFIP?
xFIP (Expected FIP) goes one step further by replacing actual home runs allowed with an expected number based on fly ball rate and the league-average HR/FB ratio. This accounts for the fact that HR/FB rates fluctuate significantly from year to year and are partly luck-driven. xFIP is an even better predictor of future performance than FIP.
Can FIP be used for relief pitchers?
Yes, but with caveats. Relief pitchers face fewer batters, so small-sample issues are amplified. A reliever's FIP over a single season (60-70 innings) will be less stable than a starter's FIP over 180+ innings. For relievers, it is best to use multi-year FIP samples or supplement with other metrics like xFIP and SIERA.