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FIP.

Fielding Independent Pitching (FIP) measures what a player’s ERA should have looked like over a given time period, assuming that performance on balls in play and timing were league average. Back in the early 2000s, research by Voros McCracken revealed that the amount of balls that fall in for hits against pitchers do not correlate well across seasons. In other words, pitchers have little control over balls in play. McCracken outlined a better way to assess a pitcher’s talent level by looking at results a pitcher can control: strikeouts, walks, hit by pitches, and homeruns.

A walk is not as harmful as a homerun and a strikeout has less impact than both. FIP accounts for these kinds of differences, presenting the results on the same scale as ERA. It has been shown to be more effective than ERA in terms of predicting future performance and has become a mainstay in sabermetric analysis.

For those curious, here’s the formula for FIP:

FIP = ((13*HR)+(3*(BB+HBP))-(2*K))/IP + constant

The constant is solely to bring FIP onto an ERA scale and is generally around 3.20. You can find historical FIP constant values here, or you can derive the constant by taking league-average FIP and subtracting that from league-average ERA.

Context:

Please note that the following chart is meant as an estimate, and that league-average FIP varies on a year-by-year basis so that it is always the same as league-average ERA. To see the league-average FIP for every year from 1901 to the present, check the FanGraphs leaderboards.

Rating FIP

Excellent 2.90

Great 3.25

Above Average 3.75

Average 4.00

Below Average 4.20

Poor 4.50

Awful 5.00

Things to Remember:

● Voros McCracken’s research was called Defense Independent Pitching Theory (DIPs Theory). It’s the building block of much of today’s pitching analysis. It can be a tricky concept to understand and counter-intuitive for most baseball fans. Refer to our sections on DIPs, BABIP, and Luck for more information.

● FIP does a better job of predicting the future than measuring the present, as there can be a lot of fluctuation in small samples. It is less effective in describing a pitcher’s single game performance and is more appropriate in a season’s worth of innings.

xFIP.

Expected Fielding Independent Pitching (xFIP) is a regressed version of FIP, developed by Dave Studeman from The Hardball Times. It’s calculated in the same way as FIP, except it replaces a pitcher’s home run total with an estimate of how many home runs they should have allowed. This estimate is calculated by taking the league-average home run to fly ball rate (~9-10% depending on the year) and multiplying it by a pitcher’s fly ball rate.

Home run rates are generally unstable over time and fluctuate around league-average, so by estimating a pitcher’s home run total, xFIP attempts to isolate a player’s ability level. A pitcher may allow home runs on 12% of their flyballs one year, then turn around and only allow 7% the next year. HR/FB ratios can be very difficult to predict, so xFIP attempts to correct for that.

Here is the full formula for xFIP. Notice how it is almost exactly the same as the formula for FIP, with the lone difference being how each accounts for home runs:

xFIP = ((13*(Flyballs * League-average HR/FB rate))+(3*(BB+HBP))-(2*K))/IP + constant

The constant is solely to bring FIP onto an ERA scale and is generally around 3.20. You can find historical FIP constant values here, or you can derive the constant by taking league-average FIP and subtracting that from league-average ERA. League-average home run per fly ball rate varies on a yearly basis, but you can find those values here on the FanGraphs leaderboards.

Along with FIP, xFIP is one of the best metrics at predicting a pitcher’s future performance. Since it was created, though, there have been some studies that suggest certain pitchers can post lower-than-average HR/FB rates over time. For more information on this, see the statistic SIERA.

Context:

Please note that the following chart is meant as an estimate, and that league-average xFIP varies on a year-by-year basis so that it is always the same as league-average ERA. To see the league-average xFIP for every year from 1901 to the present, check the FanGraphs leaderboards.

Rating xFIP

Excellent 2.90

Great 3.25

Above Average 3.75

Average 4.00

Below Average 4.20

Poor 4.50

Awful 5.00

Things to Remember:

● While HR/FB ratios are generally unstable over time, some pitchers are still more prone to allowing home runs than others. If a pitcher has a long history of over- or under-performing the league average with their HR/FB rate, then you can reasonably expect them to perform closer to their career average than the league-average. In cases like this, xFIP may overestimate or underestimate a player’s true talent level by assuming a league average HR/FB ratio. Again, for more, see SIERA.

● Ground ball pitchers typically have higher HR/FB ratios than fly ball pitchers.

● xFIP has one of the highest correlations with future ERA of all the pitching metrics. Only SIERA out-paces it.

I haven't seen/heard his starts live but I've seen the majority of them in the days after. He has the look like he's figured it out for the most part.