Back to Basics: What is Fielding Independent Pitching (FIP)?

Fielding Independent Pitching (FIP) is a stat that is used to evaluate pitching performance, similar to ERA. Unlike ERA, however, FIP attempts to isolate pitching performance from field performance/defense. Sometimes FIP can very different from ERA for a pitcher, which can be very telling. So let’s dive in and learn more about what FIP is, how it is calculated, and how you can use it.

What is FIP?

FIP is a pitching metric that only considers outcomes that are independent of defense. This means that the only outcomes included in the calculation are the ones that the pitcher is directly responsible for. These outcomes include:

• Strikeouts
• Walks
• Hit by Pitches
• Home Runs

These are the only outcomes considered because pitchers have very little control over what happens once the ball is put in play and becomes the defense’s responsibility.

Now that being said, we can’t just ignore how many singles, doubles, and triples a pitcher gives up. So to account for all hits that the defense participates in, a FIP constant is added. The constant is based on league average results on balls in play and league average timing.

What is the Formula for FIP?

What are the typical values of the FIP constant?

In recent years, the FIP constant has been around 3.10-3.20. You can find the values for each year here (under column cFIP).

You can also calculate the FIP constant yourself using the formula below:

ERA is included in this calculation because ERA and FIP are both pitching stats that are often used in conjunction with each other (Read more below about their relationship). League average FIP from year to year is designed to be the same as the league average ERA from year to year.

How do you use FIP to evaluate a pitcher?

The same way you would use ERA! The lower the FIP, the better the pitching performance.

One thing you should do, however, is compare the pitcher’s FIP to his ERA. They should be very similar. If they differ by a significant amount (1 or more), I recommend looking more into the pitcher. In the most basic sense, differences result from:

• If a pitcher’s defense is below league average, his FIP might be lower than his ERA
• If a pitcher induces more balls in play (weak contact or fly balls), his ERA might be lower than his FIP

How is FIP different from ERA?

The major difference is that ERA considers total earned runs, regardless of how they are scored. Conversely, FIP identifies how the runs are scored and isolates the ones that the pitcher is directly responsible for.

The calculation for ERA is as follows:

While FIP and ERA are both good and simple ways to evaluate a pitcher, FIP is proven to be more telling of the pitcher’s actual pitching ability.

If a pitcher has league average defense and league average timing, then FIP and ERA will be very similar.

FIP Leaders vs ERA Leaders 2019

If we compare FIP leaders vs ERA leaders from 2019, we see two different lists.

If we take this players and compare their ERA to their FIPs, we see that most of them are not significantly different.

Negative values indicate that a player has a higher FIP than ERA.

The most significant differences between ERA and FIP occur for pitchers at the end of the list, particularly Ryu, Soroka and Flaherty (red text in table).

Why do significant differences between ERAs and FIPs occur?

It is more common for pitchers to record lower FIPs than ERA, because that indicates that their defense may be impacting their earned run totals. But why would ERA ever be lower than FIP?

This goes back to the type of pitcher. If a pitcher generates weak/soft contact or more fly balls than average, their balls in play will more often result in outs. These types of pitchers can be exceptions to the FIP vs ERA debate, because FIP alone would not paint a full picture of their performance.

If we look at Hyun-Jin Ryu’s FIP and ERA, we see that his ERA is much lower than his FIP. Ryu is one of the best pitchers in the league at inducing weaker contact. While his FIP is still at the top of the league, in order to properly analyze him, you would need to dig in a little more to the type of the pitcher he is (weak contact). He is an example of a pitcher whose FIP does not necessarily tell the whole story. You would have to compare his FIP and ERA, and then dig into why they differ so much.

If we look at Gerrit Cole or Jacob deGrom, however, we see that their FIPs and ERAs are very similar. They are both strikeout pitchers (outcomes directly under their control). In this case, FIP alone would be an appropriate quick method of analyzing their ability.

Back to Basics

While a pitcher is on the mound, there are a lot of factors that determine his results. Command and velocity are a big part of how well he does day to day, but we can’t forget about luck and how the defense is performing. If a pitcher has an all-star centerfielder in the outfield, chances are he’s getting more outs than a pitcher with an average centerfielder.

So it’s not completely fair to compare those two pitchers, because the results of their pitching were not necessarily all their responsibility. And if we want to analyze one player to see how he is doing, we should be using a stat that only considers that player and what he can control.

That is what FIP attempts to do. It works with league average ERA and results to account for all balls in play that the defense participates in. And then it isolates what the pitcher’s results are on outcomes that can directly attributed to the way he is pitching.

FIP is not perfect, and should be compared to ERA in order to determine if there are other factors that need to be considered while evaluating a pitcher. It is, however, a proven indicator of a quality pitcher.

Do you have any questions about FIP? Let me know in the comments below.