Coors Field and Ground Already Trod

Back in November, I wrote about Coors Field. I noted that it's favorable for hitters not only because batted balls carry better there, which is kind of Physics 101, but also that pitches with movement, like curveballs, don't break as much, making them easier to hit. 

It turns out I wasn't being particularly original in my analysis. Last April, this article appeared by Dan Rozenson at Baseball Prospectus. It gets into some technical detail about how pitches move (you'll learn the term "spin deflection," among others), with the conclusion that: 

There is strong evidence that the slider performs in absolute and comparative terms better than the curveball in Coors Field . . . Sinking fastballs also have a sharp drop-off in performance at Coors, and there is some evidence that using a cut fastball would be a good alternative.

With that in mind, let's break down the Rockies' starters last year, using pitch type analysis from Brooks Baseball, with a particular eye toward slider usage:

• Jhoulys Chacin (31 games started, 14-10, 3.47 ERA, 1.26 WHIP): 34% fastballs, 29% sinkers, 24% sliders, 9% changeups, 4% curveballs. His slider, a good pitch for Coors, was particularly effective (.171 batting average, .286 slugging). He may not fare so well in 2014 with his sinker, though (.250 batting, .359 slugging) given that pitch's Coors performance.
• Jorge de la Rosa (30 GS, 16-6, 3.49 ERA, 1.38 WHIP): 44% fastballs, 28% splitters, 14% sliders, 7% sinkers, 7% curves. The BP article doesn't reference splitters, but since they rely on a lot of horizontal movement, you'd think they'd fare poorly at Coors. It was OK last year, though (.255 batting average, .358 slugging) and, combined with his outstanding slider (.165 batting, .194 slugging), he seems to have the right arsenal for his ballpark.
• Juan Nicasio (31 GS, 9-9, 5.14 ERA, 1.47 WHIP): 67% fastballs, 20% sliders, 7% sinkers, 6% changeups. Nicasio's slider is his primary off-speed pitch and he used it far more at home than on the road He's only 27 but his strikeouts were down, his walks up, and his fastball velocity ebbing (average 94.7 mph in 2011, 94.1 in 2012, 92.6 in 2013), so pitch selection doesn't tell the story of his 5+ ERA.
• Tyler Chatwood (20 GS, 8-5, 3.15 ERA, 1.43 WHIP): 42% sinkers, 30% fastballs, 12% sliders, 12% curves, 4% changeups. Chatwood's go-to pitch is his sinker, which isn't a great pitch at Coors. Batters had a .327 batting average and .467 slugging percentage against it, while is slider had the best results (.183 batting, .217 slugging, and an outstanding 41% rate of swings-and-misses on swings). More reliance on the slider, which he used primarily only when ahead on the count, would help, because that ERA and won-lost record look lucky given his high WHIP.

Predictions based on this: Chacin regresses a bit, de la Rosa doesn't much, Nicasio improves a little provided he isn't hurt, and Chatwood, if he goes to his slider more, is able to avoid some of the seemingly inevitable rise in his ERA.

Incidentally, did you know that in their 21 years, the Rockies have had only seven winning seasons? The only teams (among the 28 that existed in 1993) with fewer are the Orioles, Royals, Marlins, Brewers, and Pirates.

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.