Monday, November 25, 2013

Coors Field: Easy on Hitters or Tough on Pitchers?

Coors Field, home of the Colorado Rockies, is the best hitters' park in the majors. The new Bill James Handbook gives it a Park Factor of 127 for run scoring, which means that 27% more runs were scored in Rockies games at Coors than elsewhere last year. And this isn't a surprise. Denver, as you may have heard, is a mile high. The higher the altitude, the thinner the air, and the better a baseball carries. This is Physics 101. Fly balls and line drives at Coors go farther, inflating offense.

I thought that was the whole story, but recently, while listening to MLB Network Radio on SiriusXM, one of the morning hosts, former major leaguer Todd Hollandsworth, said that pitchers are challenged additionally because their secondary pitches don't have as much movement. In other words, everything pitchers throw other than a fastball is straighter at Coors. That makes it more hittable, and forces pitchers to rely more on their fastball, which hitters can time better...all bad. 

I hadn't heard the pitch movement theory before, so I decided to test it. We can do that now. Every pitch in the majors is recorded: its speed, whether it's a strike or a ball, whether it's hit, and, relevant to this question, how much it moves.

Specifically, the system, called PITCHf/x, is a set of cameras installed at every stadium that measures, among other things, the horizontal and vertical movement of every pitch. I looked up the logs of every game pitched by the Rockies' principal starters and checked how much their non-fastball pitches moved, home and away. (The source for all data in this article is Brooks Baseball.) For example, the Rockies' No. 1 starter was Jhoulys Chacin (31 games started, 14-10, 3.47 ERA, 1.26 WHIP). His main secondary pitch is a sinking fastball. In 18 home starts, he threw 449 sinkers. In 13 road starts, he threw 388. At home, Chacin's sinker moved, on average, 0.94 fewer inches horizontally and dropped 1.31 fewer inches vertically. Here's the whole story on what Coors did to Chacin's secondary pitches:

Pitch Type   # Home/Away  Horizontal Impact   Vertical Impact
Sinker         449/388        -0.94              -1.31
Slider         420/289        -2.22              -0.45
Changeup       166/92         -1.15              -1.01
Curveball       37/70         -2.50              -2.02
The impact is the change in inches between Coors and road games. A negative number means less movement, a positive number means more. Looking at these numbers, the thin air appears to make it harder to get side-to-side movement and to make balls sink, at least for Chacin. Let's check the rest of the staff:

Juan Nicasio (31 GS, 9-9, 5.14 ERA, 1.47 WHIP)
Pitch Type   # Home/Away  Horizontal Impact   Vertical Impact
Slider         255/310        -0.84              -1.95
Sinker          37/170        -0.56              +0.50
Changeup        85/88         -0.36              -0.78

Jorge de la Rosa (30 GS, 16-6, 3.49 ERA, 1.38 WHIP)
Pitch Type   # Home/Away  Horizontal Impact   Vertical Impact
Splitter       400/380        -2.13              -0.42
Slider         190/206        +0.09              -0.83
Sinker          89/99         -2.89              -1.71
Curveball       65/118        -0.36              -2.10

Tyler Chatwood (20 GS, 8-5, 3.15 ERA, 1.43 WHIP)
Pitch Type   # Home/Away  Horizontal Impact   Vertical Impact
Sinker         420/314        -1.75              -1.14
Curveball      121/94         -1.38              -2.99
Slider         126/84         -0.97              -1.72
Changeup        32/34         -1.76              -0.68

Jon Garland (12 GS, 4-6, 5.82 ERA, 1.59 WHIP) 
Pitch Type   # Home/Away  Horizontal Impact   Vertical Impact
Sinker         145/161        -0.72              -1.51
Cut Fastball   116/66         +0.69              -1.52
Curveball       65/90         -3.33              -2.04
Changeup        49/47         -0.61              -1.71

Jeff Francis (12 GS, 3-5, 6.27 ERA, 1.61 WHIP)
Pitch Type   # Home/Away  Horizontal Impact   Vertical Impact
Sinker         283/219        -1.37              -0.95
Curveball      138/80         -1.09              -0.83
Changeup       121/64         -1.01              -0.78
Cut Fastball    62/24         -0.89              -0.39

What can we learn from this? I'd say four things:
  1. There sure are a lot of negative numbers in the horizontal column! Coors does appear to impair side-to-side movement on pitches.
  2. Same with the vertical column. Pitches thrown at Coors stay up in the strike zone more. That's not necessarily bad with some pitches, which are designed to stay high, like a fastball. But a curveball that doesn't drop is a slow pitch in the middle of the strike zone. 
  3. The least affected is were Juan Nicasio and Jeff Francis, who lost an inch or less of movement on most pitches. They didn't have particularly dominant seasons, though. It's not like they cracked the code.
  4. I'm definitely paying more attention to Todd Hollandsworth going forward, because he nailed this one. Coors definitely helps batted balls carry, but it also makes it harder for pitchers to get movement on the pitches, making the hitters' job easier still.

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