What Does Coors Field Do to Pitch Selection?

I’ve got Coors Field on the mind. And while usually I’m able to flit from one subject to another — probably too easily, to be honest — when I think about Coors, it tends to stick, because the Rockies are one of baseball’s greatest experiments and we still aren’t quite sure what to make of them or what to make of baseball at altitude. The game that’s played within Coors Field is recognizably baseball, of that there’s no question, but it’s the oddest brand of baseball that exists in the major leagues, so it’s fascinating to consider as many angles as is possible. Just what is it really like to play there?

For this post, I want to examine pitch selection. And not just for pitch-selection’s sake; this should, in theory, reflect what effects people think Coors has on pitching. There’s a thought out there that Coors is bad news for breaking balls. What would we expect, then? A reduction in breaking-ball rate in Colorado, because teams and pitchers aren’t idiots. Let’s say Pitcher B has an optimal mix of 60% fastballs, 20% breaking balls, and 20% offspeed pitches. Let’s say he senses that he doesn’t have a good breaking pitch on a particular day. Then we might expect, I don’t know, 65% fastballs, 10% breaking balls, and 25% offspeed pitches. That’s the theory. So what do we see in Colorado? That’s what these big giant tables are for.

Using Baseball Savant, I grabbed home and road data, and I split the information by count types. I also categorized the pitches by pitch types, as is done over at Brooks Baseball. The data covers the PITCHf/x era from 2008 – 2014, and while it isn’t perfect to compare raw home and raw road numbers — pitchers didn’t pitch equal numbers of innings home and away — the sample sizes should limit the amount of noise. In this first big giant table, you see information for Rockies pitchers:

What do you notice? That’s right, hardly anything! I mean, there are a lot of numbers in there, but the differences are all small. The biggest difference is in the lower left. In pitcher-friendly counts, at home, Rockies pitchers have thrown slightly fewer fastballs, and slightly more breaking balls. No other difference is as large as a percentage point.

This is, I think, more interesting than it lets on. Overall, Rockies pitchers pitch at home very similarly to how they pitch on the road. Yet, while you’d expect that for most teams, the Rockies play in the most unusual home environment in the league, so you might’ve expected to see some actual adjustments. The Rockies have spent years and countless hours trying to figure out pitching a mile up. You’d think that, if they believed altitude was bad for breaking balls, there would be fewer breaking balls thrown at altitude. You’d expect a different mix to reflect consensus opinion. It would trickle down from the analysts to the on-field performance. What we see is practically no change at all. Which doesn’t mean altitude isn’t bad for breaking balls; it suggests altitude is more or less equally bad for pitches across the board. That, or, the Rockies just haven’t pitched optimally. I’m skeptical — they’ve got a lot invested in this. It’s literally their entire product.

Now then! Information for Rockies hitters, or, if you prefer, opposing pitchers:

Here, there’s a little more. All the individual differences are below three percentage points in magnitude, but, look in the middle. Opposing pitchers have thrown more breaking balls in Colorado in all situations. They’ve come at the expense of both fastballs and offspeed pitches. The first thing that might indicate is that even visiting pitchers don’t feel like their breaking balls are being particularly affected. If anything, it’s the opposite of that. And then, consider the differences between this table and the table above. Rockies pitchers are more incentivized to learn how to pitch in Colorado than non-Rockies pitchers. Given that Coors Field is so unusual, you’d think Rockies pitchers would better understand optimal pitching at altitude. Rockies pitchers don’t increase breaking balls at home very much. Opponents have shown a bigger change. That might have just a little something to do with Colorado’s significant home-field advantage.

There’s one last little thing I want to touch on, that’s tangentially related to the above. What you’ve seen is all about pitch mix. What about pitch location? For these purposes, imagine a horizontal line, 2.5 feet above the ground at the front of the strike zone. I’m going to use this line to split pitch location in half, with pitches being either up or down. Great, now, think about secondary pitches, or all the pitches that aren’t fastballs. Most of the time, you want those pitches to be down — left up, they might steal called strikes, but more often they look like hangers. Changeups, sliders, curveballs, splitters…you almost always want these in the vicinity of the lower zone border.

In home games, Rockies pitchers have thrown 69% of their secondary pitches down, which ranks them 23rd in baseball. On the road, they’re at 72%, ranking 9th in baseball. Now, in home games, Rockies hitters have seen just under 66% of secondary pitches down, ranked 30th in baseball. Away from home, that’s gone up to 70%, which is right in the middle of the pack.

This might be nothing more than a simple PITCHf/x park effect. I don’t actually know. Maybe there’s something about the system that spits out slightly higher vertical locations. But the alternate explanation would be that, in Colorado, it’s just a little harder to keep pitches down, especially the pitches you want to keep down. Which would leave more of those secondary pitches vulnerable. Rockies hitters might’ve been feasting on slower stuff that was supposed to be lower than it actually was. Could help explain the reduced strikeouts. Could help explain a lot of things. Wouldn’t explain the subtle changes in pitch mix we saw in the tables, but, who knows? The whole thing remains kind of a mystery.

There’s nothing quite like baseball in Denver. That’s not true. There’s even baseball over in Colorado Springs. But, there’s nothing in the majors quite like baseball in Denver. It’s a challenging thing to get used to. And then, very suddenly, a player has to get un-used to it. I’m glad such an experiment exists. I’m also glad I’m in no way involved with it.