This has been mentioned in a couple of threads on the Red Sox thinking this offseason, and I thought it was worthy of a more comprehensive analysis than I had seen to date.
As many know, the strike zone looked a little different in 2014 than it did in 2013. I'll quote the New York Times from this October on the subject:
The general decline of offense in favor of pitching is one obvious consequence of an enlarged strike zone, but having it the strike zone expand the lower part of the zone should also benefit certain kinds of pitchers over others. Specifically, the low strike zone should work to the benefit of low in the zone, ground ball pitchers. That is, the kind of pitchers the Red Sox have been acquiring this offseason.
A secondary question is how the impact of increased use of defensive shifts might have an impact on the performance of ground ball pitchers. Are ground ball pitchers disproportionately benefiting from shifts?
So I thought I'd take a look at the top groundball pitchers in baseball and see if, as a group, they had significantly achieved an improvement in their performance between 2013 and 2014. Here are all the pitchers in MLB who had a 53% GB rate in 2014 and had enough innings in 2013 to provide a decent enough sample for that year:
Here are those same pitchers during 2013:
Here is the difference between their 2014 performance and their 2013 performance, in %
Overall, ERA improved by 14% from 2013 to 2014, while xFIP improved a more modest 5%. K/9 improved 4%, but BB/9 had the biggest impact - exactly what you'd be looking for for strike zone differences, with a 13% drop in BB/9. This chart has HR/9 jumping by 22% as well, although all of that jump comes from Henderson Alvarez, whose HR/9 jumped from an obviously unsustainable .18 in 2013 to .66 in 2014. Remove Alvarez and the HR/9 rate of the others improved by 6%.
It's too limited a set of data to draw firm conclusions, but a 13% drop in BB/9 spread out among a pretty significant set of starters seems significant, although there may be a little bit of selection bias. I'm particularly impressed at the number of starters who went from having good control to great control. Keutchel drops by 95 points, Alvarez from 2.37 to 1.59, Hudson from 2.47 to 1.62. Hernandez from 2.03 to 1.75. Only the erratic Liriano moves significantly in the other direction on BB/9.
I think these numbers could also suggest that shifts could be having some impact. Out of the 10 pitchers 5 had ERAs that outperformed their xFIP, with only Leake going significantly the other way. You look at the teams that employ the most defensive shifts and I see some overlap with the pitchers with good differentials there although the relationship isn't clear.
As many know, the strike zone looked a little different in 2014 than it did in 2013. I'll quote the New York Times from this October on the subject:
The strike zone is bigger than it used to be, especially around batters’ knees.
The change appears to stem from the league’s growing use of video technology to evaluate umpires, which has led umpires to stick more closely to the official strike zone. And according to the rule book, the strike zone extends down to “the hollow beneath the kneecap.” The enlarged strike zone, in turn, seems to be a major reason that strikeouts have risen and scoring has dropped sharply.
Two different analyses of pitch-tracking software have found that the strike zone has grown almost 10 percent over the last five years. It grew in each of the last five seasons and more in 2014 than in any previous season. Five years ago, pitches just below 21 inches high and over the plate were rarely called strikes. This season, they usually were, according to one of the analyses, by Jon Roegele, which appeared in the publication Hardball Times.
“The strike zone has increased in size significantly,” said Brian Mills, a professor of sports management at the University of Florida, and the author of the other analysis, “and it’s had a huge impact on run scoring over the past eight years or so.”
The general decline of offense in favor of pitching is one obvious consequence of an enlarged strike zone, but having it the strike zone expand the lower part of the zone should also benefit certain kinds of pitchers over others. Specifically, the low strike zone should work to the benefit of low in the zone, ground ball pitchers. That is, the kind of pitchers the Red Sox have been acquiring this offseason.
A secondary question is how the impact of increased use of defensive shifts might have an impact on the performance of ground ball pitchers. Are ground ball pitchers disproportionately benefiting from shifts?
So I thought I'd take a look at the top groundball pitchers in baseball and see if, as a group, they had significantly achieved an improvement in their performance between 2013 and 2014. Here are all the pitchers in MLB who had a 53% GB rate in 2014 and had enough innings in 2013 to provide a decent enough sample for that year:
2014 | ||||||
ERA | FIP | K/9 | BB/9 | HR/9 | GB% | |
Keuchel | 2.93 | 3.2 | 6.57 | 2.16 | 0.5 | 63.5 |
Ross | 3.17 | 3.11 | 8.97 | 3.31 | 0.6 | 57 |
Hernandez | 2.14 | 2.51 | 9.46 | 1.75 | 0.61 | 56.2 |
Cobb | 2.87 | 3.33 | 8.06 | 2.54 | 0.6 | 56.2 |
Liriano | 3.02 | 3.4 | 9.7 | 4.49 | 0.72 | 54.4 |
Wheeler | 3.54 | 3.49 | 9.08 | 3.84 | 0.68 | 54 |
Alvarez | 2.65 | 3.57 | 5.34 | 1.59 | 0.67 | 53.8 |
Peralta | 3.53 | 3.64 | 6.98 | 2.76 | 1.04 | 53.6 |
Leake | 3.7 | 3.49 | 6.89 | 2.1 | 0.97 | 53.4 |
Hudson | 3.57 | 3.57 | 5.7 | 1.62 | 0.71 | 53.1 |
Here are those same pitchers during 2013:
2013 | ||||||
ERA | FIP | K/9 | BB/9 | HR/9 | GB% | |
Keuchel | 5.15 | 4.25 | 7.2 | 3.05 | 1.17 | 55.8 |
Ross | 3.17 | 3.43 | 8.57 | 3.17 | 0.58 | 54.9 |
Hernandez | 3.04 | 2.66 | 9.51 | 2.03 | 0.66 | 51.4 |
Cobb | 4.03 | 3.02 | 8.41 | 2.83 | 0.82 | 55.8 |
Liriano | 3.02 | 3.12 | 9.11 | 3.52 | 0.5 | 50.5 |
Wheeler | 3.42 | 3.49 | 7.56 | 4.14 | 0.9 | 43.2 |
Alvarez | 3.59 | 3.97 | 5 | 2.37 | 0.18 | 53.5 |
Peralta | 4.37 | 4.13 | 6.33 | 3.58 | 0.93 | 51 |
Leake | 3.37 | 3.91 | 5.71 | 2.25 | 0.98 | 48.7 |
Hudson | 3.97 | 3.56 | 6.51 | 2.47 | 0.69 | 55.8 |
Here is the difference between their 2014 performance and their 2013 performance, in %
Difference | ||||||
ERA | FIP | K/9 | BB/9 | HR/9 | GB% | |
Keuchel | 57 | 75 | 91 | 71 | 43 | 114 |
Ross | 100 | 91 | 105 | 104 | 103 | 104 |
Hernandez | 70 | 94 | 99 | 86 | 92 | 109 |
Cobb | 71 | 110 | 96 | 90 | 73 | 101 |
Liriano | 100 | 109 | 106 | 128 | 144 | 108 |
Wheeler | 104 | 100 | 120 | 93 | 76 | 125 |
Alvarez | 74 | 90 | 107 | 67 | 372 | 101 |
Peralta | 81 | 88 | 110 | 77 | 112 | 105 |
Leake | 110 | 89 | 121 | 93 | 99 | 110 |
Hudson | 90 | 100 | 88 | 66 | 103 | 95 |
Average | 86 | 95 | 104 | 87 | 122 | 107 |
Overall, ERA improved by 14% from 2013 to 2014, while xFIP improved a more modest 5%. K/9 improved 4%, but BB/9 had the biggest impact - exactly what you'd be looking for for strike zone differences, with a 13% drop in BB/9. This chart has HR/9 jumping by 22% as well, although all of that jump comes from Henderson Alvarez, whose HR/9 jumped from an obviously unsustainable .18 in 2013 to .66 in 2014. Remove Alvarez and the HR/9 rate of the others improved by 6%.
It's too limited a set of data to draw firm conclusions, but a 13% drop in BB/9 spread out among a pretty significant set of starters seems significant, although there may be a little bit of selection bias. I'm particularly impressed at the number of starters who went from having good control to great control. Keutchel drops by 95 points, Alvarez from 2.37 to 1.59, Hudson from 2.47 to 1.62. Hernandez from 2.03 to 1.75. Only the erratic Liriano moves significantly in the other direction on BB/9.
I think these numbers could also suggest that shifts could be having some impact. Out of the 10 pitchers 5 had ERAs that outperformed their xFIP, with only Leake going significantly the other way. You look at the teams that employ the most defensive shifts and I see some overlap with the pitchers with good differentials there although the relationship isn't clear.