Advanced Stats 102: FIP and xFIP

Today we are going to dive into FIP and xFIP. These two stats are incredibly useful in deducing how a pitch performs based on his performance, not the performance of the guys playing the field behind him. SDI Staff Writer Eddie Middlebrook is the site guru on FIP and xFIP, and you’ll see that term thrown around quite a bit when discussing pitching with him. This article is basically an introduction to these two stats, so if you need any further explanation, Eddie is the go to guy.
FIP (Field Independent Pitching)

FIP tells you how a pitcher should have performed, not how he actually performed. Confused? Let me explain. A pitcher can only control certain aspects of a game: such as walks, hit batters, wild pitches, etc. What FIP does is takes away the team performance behind the pitcher, and tells us what the pitcher’s ERA should have looked like over a period of time without using defensive statistics. So basically, FIP takes what a pitcher can control, walks, home runs, etc and predicts that players true talent level. One thing to remember in FIP is that the larger the sample size, the more accurate the stat becomes.

The formula for FIP is: ((13 x HR) + (3 x (BB + HBP – IBB)) – (2 x K)) / IP + constant

* The constant is merely a number in order to place FIP on the same scale as ERA. It is usually between 3.15- 3.20.

So in a nutshell, FIP takes away the defense’s impact on a pitcher and tells us the story of the pitcher’s performance based only on what the pitcher has control over. It we reverse the nomenclature to “Pitching Independent of Fielding”, that may help explain it better.  For example:

. 2012 IP K/9 BB/9 HR/9 ERA FIP
. Matt Harrison 213.1 5.61 2.49 0.93 3.29 4.03
. Yu Darvish 191.1 10.4 4.19 0.66 3.90 3.29
So, based solely on each individual alone, we can see that, independently, Yu was a little more effective, in FIP. This does not mean that Darvish is far and away better than Harrison. If we look at the K/9 rates between the two pitchers, you can see the difference in FIP. More balls are put in play off of Harrison, who is a ground ball pitcher, and Darvish is becoming a strike out pitcher, thus his FIP is lower. Just remember, the lower the FIP, the better the pitcher is at creating his own outs.

xFIP (Expected Field Independent Pitching)

xFIP is almost the same as FIP, except that xFIP factors in how many home runs the player should have allowed. xFIP replaces the number of home runs a pitcher gave up with an estimate of how many they are expected to surrender. This one is a little more difficult to understand, because it uses HR/FB% (home run to fly ball). 

Here is the formula: xFIP = ((13*(FB% * League-average HR/FB rate))+(3*(BB+HBP))-(2*K))/IP + constant

We’ll use Matt Harrison again as our example:

. Matt Harrison K/9 BB/9 HR/9 ERA FIP xFIP
. 2011 6.11 2.76 0.63 3.39 3.52 3.85
. 2012 5.61 2.49 0.93 3.29 4.03 4.13
What xFIP does, is to take a pitchers HR/FB rate and it replaces it with the league average HR/FB rate. For example, Matt Harrison gave up home runs on 7% of fly balls in 2011, but then on 10% in 2012. What xFIP does, is removes that percentage and replaces with that year’s league average to isolate a pitchers true value. So, to break this down into English, xFIP is an expected FIP based on a league average of HR/FB rates. It’s an expectation of a pitchers value.

So, in summation, both FIP and xFIP are studies of a pitcher’s own ability and takes away any help from his defense. It’s a measure of “true ERA”, based only on what that player can control, like K’s, BB’s, walks and hit batters.There are those that do not like xFIP, because it is a prediction based on fly ball rates. However, it is still valuable, since it factors in the league average. Maybe the most important thing to remember about FIP and xFIP, is that the bigger the sample size, the more accurate the stat is.

Patrick Despain is the CEO and Co-Founder of ShutDown Inning. He can be reached or on Twitter @ShutDownInning
Patrick Despain
Patrick is a member of the IBWAA and creator of Shutdown Inning. He was raised him Arlington, Texas and grew up watching games on HSE and listening to Eric Nadel and Mark Holtz on the radio. He is a long time Rangers fan and never achieved his dream of being a bat boy. He know lives in Georgia with dreams of a Texas return.

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