Comparing FIPS and xFIPS Using Batted Ball Distance

In one of the World Series chats I hosted, it was stated that Matt Cain gave up weak fly balls and that is the reason that his xFIPs (2010 = 4.19 and lifetime = 4.43 ) are higher than his FIPs (2010 = 3.65, lifetime = 3.84). After finally getting all the wrinkles worked out, I am able to get the average distance for fly balls given up by a pitcher. So, does the fly ball distance given up by a pitcher help to explain the difference between his xFIPs and FIPs?

I took just the pitchers that threw over 60 innings in 2010 and subtracted their FIPs from their xFIPs. Then I got the average distance of all the fly balls for these pitchers and here are the top five leaders and laggards:

This past season it can be seen that the top five pitchers whose FIPs are lower than their xFIPs allowed fly balls to travel 26 feet less than the top five pitchers who had FIPs higher than their xFIPs. I expected to find some difference, but 26 ft per fly ball on these two groups was pretty substantial in my opinion, so I dug a little more.

One main problem I noticed immediately looking through all the data was that the Colorado pitchers had fairly high distances given their xFIP-FIP rates. I went ahead and did a small adjustment for elevation and temperature for each home park using data from Robert Adair’s “The Physics of Baseball”.

I assumed half of each player’s games were at home and all their road games were at a league-average level. With this adjustment, the Colorado pitchers came more in line. Because I adjusted for the park numbers, I removed all pitchers that swapped teams mid-season to make the analysis easier. With the new set of data, I compared the data again and got the following results.

1. The average distances of balls hit by the players with a negative xFIP-FIP is 289.3 ft while the distance hit by those with a positive xFIP-FIP is 281.6. A difference of almost eight feet.

2. Here is the list of five pitchers that threw > 160 innings (I wanted to show the top starters this time) and had the highest and lowest xFIP-FIP values:

3. The r-squared value for the second set of data is 0.23 (Tom – the R is 0.479).

There seems to be some decent correlation between how far a pitcher allows a fly ball to fly and his xFIP-FIP difference. In other words, pitchers that allow the ball not to be hit as far, don’t allow as many home runs (duh), therefore their FIP value is much lower than their xFIP.

The correlation is not great, but there is enough evidence for me to continue looking. The two main points I need to explore further are:

1. I need to get the park factors nailed down for the batted ball distance. I need to adjust every fly ball’s distance.
2. Once that is down, I need to see if there is any correlation from one season to the next for a pitcher’s fly ball distance.

So many questions, so little time.

Jeff, one of the authors of the fantasy baseball guide,The Process, writes for RotoGraphs, The Hardball Times, Rotowire, Baseball America, and BaseballHQ. He has been nominated for two SABR Analytics Research Award for Contemporary Analysis and won it in 2013 in tandem with Bill Petti. He has won four FSWA Awards including on for his Mining the News series. He's won Tout Wars three times, LABR once, and got his first NFBC Main Event win in 2021. Follow him on Twitter @jeffwzimmerman.

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Steven Ellingson
Steven Ellingson

I’m excited for #2. That’s something I’ve been wondering for a while.


Much agreed.


I Agree too.
But after all, the reason xFIP was invented, I remember, was because of the fact that there was little correlation on HR/FB between one year and the next, so I expect it has also little correlation.