The Coors Field Problem
Coors Field is bad for baseball. There’s something (or lack of something) in the mountain air that creates a dangerous imbalance in the game when teams play there. It’s not because the thin mountain air causes more home runs there, that helps both teams essentially equally and is always exciting to see. This is something different. I recently discovered this “Other Coors effect” while watching Trevor Bauer’s podcast “Bauer Bytes”. In it, Bauer and some fellow MLB players talked over dinner and for a short portion of it they conversed about playing at Coors Field. Bauer mentioned how he started a game there once and something seemed off, his pitches weren’t right. After the game he discovered that his fastball was moving three inches less than usual. The conversation was just a small part of a 30+ minute episode but that small part stuck with me and I wanted to find out more.
Research:
Upon finding out about this effect at Coors Field I immediately went to investigate it more. Using statcast’s pitch tracking and the programming language Python, I was able to quantify this effect that Bauer mentioned. I first looked at the Rockies’ top two starters Jon Gray and German Marquez and calculated the average movement of all their pitches at Coors and compared it to their movement at other stadiums.
The points that are x’s denote the average movement of the pitch at Coors while the dots denote the average movement of the pitch on the road. We immediately see some big differences. It seems that Marquez’s 4-seam, 2-seam, and changeup have a lot more vertical movement and about a quarter of a foot more tail on the road than at Coors. The effect seems to have a much more muted effect on breaking pitches like his slider and knuckle-curve though.
We see a very similar trend for Jon Gray. His fastballs and changeup all move considerably more on the road while the effect on breaking pitches is negligible.
Effect:
So what does this mean? Some of you might be thinking “Well that’s nice for them, their pitches become nastier on the road!” While there might be some truth to this, there is also a much bigger and potentially troubling effect. Imagine you’re a pitcher who doesn’t come to Coors field very often, of course you know about the effect that the high elevation has on fly balls but when you go to pitch, suddenly all your pitches aren’t rising as much and have almost a quarter of a foot less movement! There’s a popular saying that “Baseball is a game of inches” and this is even truer for pitchers. 3 inches of movement could easily be the difference between a fastball being belted over the fence and a strikeout looking on the outside corner.
Now I hear you skeptics saying “That’s just silly speculation. The effect can’t be that bad!” which to that I invite you to look back with me at June 7th 2017. This is the start that Bauer mentioned in the episode of Bauer Bytes. Being in the AL for most of his career up to this point, Bauer had never played in Coors. He was surely aware of the homerun problem at Coors but that wouldn’t be why he lost this game. He would go on to have a pretty bad game pitching 3 and 1/3 innings while walking 5 batters and ending up with 4 earned runs. While no pitcher is immune to the odd bad game, I don’t think this outing necessarily falls under that category. I think Trevor Bauer fell victim to “The Other Coors Effect”. Bauer’s 5 walks was uncharacteristically high for him in 2017 where he put up a 3.06 BB/9. I believe that because of his inexperience playing at Coors Field, Bauer ended up walking more batters because of the effect it had on his pitch movement. The data seems to show that Bauer isn’t alone in this because in all interleague games played at Coors Field from 2015–2019, opposing teams walked Rockies batters an average of 3.22 times per game. However, in interleague games where the Rockies were visiting, Rockies batters were only given a free pass 2.36 times per game. That’s essentially 1 free baserunner more for the Rockies when playing at home. Not only does this affect the amount of times Rockies players are walked, but I also believe that it exacerbates the already unusually large offensive advantage at Coors Field. Because visiting pitchers are unaccustomed to the mountain air’s effect on their pitches, they are more likely to fall behind in counts, this in turn puts Rockies players in more situations where they can get better pitches to hit. This also disproportionately affects pitchers that rely on precision rather than their ability to overpower hitters. A few victims of this are pitchers like Hyun-Jin Ryu and Zack Greinke. I chose to highlight Greinke and Ryu because they have played large parts of their careers in the NL west and are both known for their ability to locate pitches. One more thing they have in common is their susceptibility to “The Other Coors Effect”. Because they both rely on their ability to expertly locate their pitches, the effect that Coors Field has on their pitch movement seems to cause them to struggle more. Ryu for example has a whopping .342 OPP BA and a BB/9 of 4.1 at Coors field whereas when he plays at his former home stadium in LA he has a .247 OPP BA and a BB/9 of 1.7. Greinke’s splits aren’t as drastic but he still shows signs of struggle in Coors with a 2.4 BB/9 and .290 OPP BA compared to his 1.9 BB/9 and .226 OPP BA in LA and AZ. Of course, the offensive advantage of playing at Coors definitely plays a part in their inflated numbers, but it’s definitely not the only factor. The fact is that pitchers like Greinke and Ryu are seriously disadvantaged at Coors Field and their stuff just isn’t as effective as it is in other stadiums.
Conclusion:
These findings raise a troubling question: Do the Rockies have an unfair advantage at Coors Field? Of course, everyone has a slight edge playing at home. You have more fans, you know the field better, and you get to bat at the bottom of the inning, but these are all relatively minor advantages. Coors Field is an atypical case. Every stadium has its quirks like Fenway Park with the Green Monster in left and the short porch in right and Wrigley Field has its famous ivy wall. These offer advantages to players with more experience in the stadium who know how the ball will bounce off the wall or where the wall is when chasing down a flyball but Coors Field is a completely different environment. Not only does it affect the pitchers but the elevation makes it hard for all players that are unaccustomed to playing 1 mile above sea level to adjust. Their own players are much more accustomed to adjusting to the change in elevation and the pitchers likely even have strategies in place to counteract the effects of the mountain air. It’s clear that the Rockies have a bigger advantage at home than any other team. Is it too much? I think so. Just the fact that there is no other stadium with this effect makes it unfair and creates anomalies. Unless you are a sabermetric nerd like Trevor Bauer or consistently playing at Coors Field, you most likely won’t even notice the Coors Effect. Visiting pitchers that come to Coors Field once a year and experience the effect on their pitches probably assume that they had a bad day and that their pitches were off. Trevor Bauer didn’t even notice it until after the game when he looked at his analytics but the effect still has an impact even when pitchers don’t notice it.
As to potential solutions to the Coors Problem, I don’t really have any. Moving to a city with a lower elevation seems drastic and very unlikely and other options would most likely require a sizable financial investment.
Do you think this effect is unfair? If so, what do you think are some solutions?
References:
The plots were made using python and Statcast’s pitch-by-pitch data. I also used Baseball Reference, and Retrosheet game logs to get my data.
Links:
