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Friday 23rd Jun 2017

FIP has been a much-maligned stat in some sabermetric circles. The complaint is that FIP gives too much credit to the pitcher for preventing home runs. This gave birth to xFIP, which normalized the home run to fly ball rate to a league average. I think it’s rather intuitive that a pitcher has some influence over how frequently his fly balls leave the park and I don’t take seriously the notion that a home run rate that deviates from league average is necessarily and entirely due to just luck, park factors, and weather. If only a major league ball club would allow me to take the mound for 30 starts I could quickly dispel this notion. You would see balls leave the yard at a rate that would shatter the league average and I assure you this rate would never normalize no matter how many starts the team suffered through. This should all make sense. It takes skill to connect with a good slider and hit it on the screws. The more perfect the contact the farther it will travel. The better the breaking ball, the more likely the hitter will miss it, if only slightly. This will impact the distance on fly balls and how many will die on the warning track as opposed to clearing the fence.

Does this mean we should stick to FIP as our adjusted ERA of preference? Not necessarily. The problem is sample size. It simply takes too long to amass a sample size large enough for a HR/FB rate to give us an accurate picture of a pitcher’s home run prevention skills. By the time enough stats are accumulated, the pitcher has already gone through a number of evolutions. His velocity has increased or decreased any number of times. He may have added a new pitch, dropped another, adjusted his grip on his change up, learned how to change speeds more effectively, etc. etc. On top of this, the impact of his HR prevention skills is statistically minimal. In light of all this, it may be preferable to use xFIP.

Among qualified pitchers, Gio Gonzalez had the lowest FB rate last year, as 5.8% of fly balls left the yard. This year, he’s giving them up at a 9.6% clip (career 9.3%). Aaron Harang went from 6.3% to 11.4% (career 10.4%). Felix Hernandez posted an above average 7.7% that shot up to 11.0% this year (10.3% career). In fact, the top 10 from 2012 all follow this same pattern except for Clayton Kershaw, who has trimmed his numbers from 8.1% down to 6.6% (career 6.8%).

Pitcher

2013 HR/FB%

2013 ERA

2013        FIP

2013      xFIP

Career HR/FB %

Jhoulys Chacin

2.4

3.59

3.11

4.10

9.3

Clay Buchholz

3.2

1.71

2.48

3.22

10.2

Adam Wainwright

4.2

2.22

2.01

2.67

7.7

Lance Lynn

4.9

3.52

3.10

3.89

8.5

Matt Harvey

5.1

2.00

2.00

2.64

6.6

Eric Stults

5.1

3.51

3.26

4.21

7.8

Derek Holland

5.6

3.14

2.75

3.44

12.0

Bud Norris

5.7

3.35

3.53

4.32

10.7

Doug Fister

5.9

3.50

2.82

3.25

7.8

Jorge De La Rosa

6.0

3.09

3.49

4.03

11.0

Travis Wood

6.0

2.85

3.59

4.40

8.4

Chacin’s 2.4%, from a pitcher who pitches half his game at Coors Field, jumps off the page. Interestingly, in Colorado he’s yielding only 1.9%. It doesn’t take a sabermetrician to realize that this is unsustainable. His ground ball rate is up and his fly ball rate is down. That’s good. His strikeout rate being lower is not so good. Be prepared for a correction.

Travis Wood is another player I own that is skating on thin xFIP ice. Even if you buy into the concept of a pitcher inducing weak contact, his .218 BABIP has nowhere to go but up. Enjoy the flight while it lasts, but don’t be surprised if you encounter some turbulence before too long. Clay Buchholz owners should also brace themselves for a few bumps in the road. His luck in keeping it in the park and that .258 BABIP aren’t going to last.

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