It's a familiar story. A Rockies pitcher is having trouble pitching at home. What else is new?
Tyler Chatwood is making some waves as a member of the Rockies rotation. He leads their starters in fWAR at 1.4, though that is party due to him throwing the highest number of innings on the team. Jon Gray is nipping at his heels at 1.1 fWAR but in 25 fewer innings. Over those 77.1 innings, the righty Chatwood has a 2.79 / 3.84 / 4.14 ERA / FIP / xFIP line. His strikeout and walk rates are not especially great, just 15.7 and 7.4 percent respectively, so it's something else that's gotten him this far. Grounders.
Chatwood's 57 percent GB rate ranks 7th among qualified starters, right between Jake Arrieta and Noah Syndergaard. Arrieta and Syndergaard are good pitchers. So, on the surface, Chatwood's low BABIP and LOB% make sense. Hitters are making a bunch of soft contact (low LD rate) and pounding the ball into the ground. This is all good.
Then remember that Chatwood pitches for the Rockies, who play an approximate version of baseball that the rest of MLB plays. We all know their home park makes crazy things happen to baseballs, enough so that they keep baseballs in a thing (humidor) that also helps keep cigars fresh. Baseballs are not cigars.
Of course, there is no way of knowing if this will hold through the season, but Chatwood has the largest home/road split in baseball (among starters), depending on which metric you use.
I snagged a bunch of this season's data from FanGraphs to compare Chatwood's home/road splits to everyone else. Let's start with wOBA allowed. Chatwood's home figure is .365; his away figure is .204. That's a difference of .161, which is the largest difference (negative or positive) among the 84 pitchers in the dataset.
How about ERA? His home ERA is 5.30; his away ERA is 0.65. That's a difference of 4.65, which ranks second to only Zack Greinke among those with a higher home ERA. It ranks third by absolute value, with Chris Archer sneaking ahead of him.
How about HR/FB? His home HR/FB is 23.1 percent. His away HR/FB is zero. Chatwood has not allowed a home run away from Coors yet. That ranks number one among those with a higher home HR/FB. Only Kendall Graveman has a larger difference by absolute value. Graveman's given up 10 homers in only 28 innings away from Oakland. Yeesh.
How about FIP? Chatwood has a home FIP of 5.15 and an away FIP of 2.72, which ranks second to Greinke among those with a higher home FIP. There are actually quite a few pitchers whose away FIP is higher than their home FIP.
Lastly, how about xFIP? Chatwood has a home xFIP of 4.15 and an away xFIP of 4.13, which ranks ... wait. That's pretty much the same. In fact, if there were a leaderboard here in which we sorted by the smallest difference between home and away xFIP, Chatwood leads it.
Among his peers in low-xFIP-difference land, Chatwood BY FAR has the largest difference between his home and away HR/FB rates, which is interesting because xFIP is one of the stats adjusting for out-of-whack home run rates.
So, Chatwood has been an ace away from Coors and a typical Coors pitcher within Coors, and the difference is massive among his peers. I looked to Baseball Savant to see if there were any differences in how he uses his fastballs, which comprise a huge majority of the pitches he throws.
Home (FF and FT)
Away (FF and FT)
The obvious difference is that Chatwood targets different corners of the plate whether he is at home or away. As a righty, he's keeping his fastballs low and away against lefties and low and in against righties away from Coors. That seems pretty good. He is unable to do the same at home.
This is probably the Coors thing going on. I grabbed all of Chatwood's PITCHf/x two-seam fastballs from 2016. Despite throwing an almost equal number of total pitches home and away, Chatwood uses his two-seamer/sinker a lot less at home. He's thrown it 232 times away vs. 171 times at home.
The sinker/two-seamer is not quite the same pitch in Coors. I used a simple T test to compare the horizontal and vertical movements of his two-seamer away and at home, and the difference is incredibly statistically significant. Away from Coors, Chatwood's sinker/two-seamer gets fully two more inches of fade (-6.42 away vs. -4.39 home). Interestingly, this pitch actually gets more sink away from Coors (6.03 away vs. 7.24 home).
So, against lefties, if Chatwood is aiming for the front hip with his sinker, it's going to fade further away from lefties when he's not pitching at Coors. I think this is likely a big reason for the difference in location above.
For his four-seam fastball, the horizontal and vertical movements at home are 0.01 and 6.74, respectively. Away, they're -0.83 and 8.52. His away four-seam fastball is a better fly ball/popup pitch, which shows up in his batted ball distribution. It does not really help explain the heat maps above, since those are not split out by fastball type.
After splitting out those heat maps by fastball type, Chatwood shows confidence throwing his four-seamer to certain parts of the plate.
That's a pretty clear difference. Chatwood is trying to keep his four-seam fastball down when he's at home, but he's not afraid to throw it up when he's away from Coors.
Oh. Hey. That's interesting. Chatwood throws his two-seamer to the same corner of the plate. At home, he appears to be much more pinpoint with his control, though it appears to be less in the zone. Away, he catches more of the plate.
So the difference in the first set of heat maps, when the two fastballs were combined, is not really due to his two-seamer. It's mostly his four-seamer. However, Chatwood should be fairly aware of the Coors effect on the fade of his two-seamer. It's possible that because there is less movement and less margin for error, Chatwood has to be much more nibbly with the pitch. Away, he gets more movement, has more margin for error and can throw more strikes.
Indeed, his walk rate and strikeout rate are better away than at home, and he gets more grounders at home -- remember, he tries to keep his pitches down more when he's in Colorado. In general, a lower pitch will result in more contact and more grounders, and a higher pitch will result in more whiffs and more fly balls. Pretty simple.
Unfortunately, the Coors effect appears to be rendering Chatwood ineffective at home. There's still time for this stuff to stabilize, but funky things happen when Coors Field is involved. At least he's still an ace away from home.
. . .
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