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Change is Everywhere

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James Shields is a good pitcher.

James Shields is a good pitcher.

James Shields is a good pitcher.

But only at home?

That seems to be the trend in Shields' career. Within the confines of Tropicana Field Shields is one of the best pitchers in the league, but on the road his walk rates increase while his strikeout and groundball rates decrease. Why?

The hot theory: Shields change-up does not break quite as well in uncontrolled environments. Without rain, wind, and humidity the Rays pitchers are essentially throwing within a vacuum. Despite the decent dimensions and seemingly adequate lighting the Trop is amongst the most pitcher friendly parks in the league this season; singles, triples, strikeouts, and walks are above league average, but doubles and homeruns are well below.

To test the theory I decided to pull up his change-up's break data from home and away starts (with one exception each: the brawl game in Boston and 4/22 against Toronto, for whatever reasons the data was unavailable), just to see what the breaks looked like. Before I present the data, I would like to note a few possible explanations for the results. We obviously do not know when he "has a good feel" or not, in fact we are not even sure if that really exists. Pitchers always talk about not having their good stuff unfortunately that seems to make up 95% of their starts. How often do you hear a pitcher say "My stuff was really, really good today..." after giving up more than a few hits and runs? On the other hand, do pitchers ever say, "I just had to battle today..." after throwing a no hitter? The data also could be from a misclassification in pitch or break. PitchFx data is usually quite accurate, but mistakes do sometimes occur in classifying pitches. I do not expect that to be an issue because change-ups are not easily confusable. Note: hit the "wide" view button to see both charts fully.


Home Avg Speed H-Break V-Break Str%
Away Avg Speed H-Break V-Break Str%
Bal 82.49 -6.06 5.14 76.47
Tor 81.47 -7.43 2.21 57.69
Tor 81.81 -6.38 5.08 62.5
Oak 81.97 -7.14 3.15 59.09
Ana 80.96 -6.41 5.37 72
Sea 82.18 -7.78 3.97 72.73
Det 82.26 -7.27 5.67 67.86
Tor 81.55 -7.33 0.11 75
Oak 81.97 -6.73 4.53 66.67
Cle 83.69 -7.26 1.22 75
Tor 81.88 -6.54 4.33 48
Fla 81.27 -9.58 2.85 64
Kan 81.5 -7.18 3.12 75
Ana 82.93 -9.65 3.22 77.14
Bos 83.24 -9.85 4.14 63.64
Oak 81.33 -8.36 3.22 66.67
Chc 83.26 -9.86 3.75 69.57
Bos 82.33 -10.03 4.46 57.58
Chw 82.81 -11.23 4.03 70.37
Min 82.35 -9.04 5.57 78.13
Bal 82.68 -11.52 4.17 77.27
NY 81.99 -13.48 4.12 66.67
NY 82.47 -11.58 3.28 63.16
Bal 81.49 -7.14 4.82 68.42
Ana 82.68 -10.9 3.72 80

Bos 81.96 -10.12 3.48 77.27

Bal 81.23 -11.16 4.72 66.67

Clarifying the obvious: H-Break is the horizontal break, a negative value means it breaks TOWARDS right-handed. Imagine yourself as the catcher and there's a transparent piece of graph paper in front of you, that's exactly how this works. V-Break is vertical break and negative means it breaks down. But how can pitches break up you ask, well these are all compared to a pitch with NO spin - over 60 feet it would fall due to gravity.

Here are the averages:


Avg Speed H-Break V-Break Str%
Home 82.21 -8.85 4.3 69.1
Away 82.05 -8.69 3.24 68.2

Shields change actually breaks down MORE on the road, otherwise everything is just about equal. So what are his issues on the road exactly? Is it simply bad luck (his BABIP is .313) or just Shields doing what most pitchers do; struggle on the road?