Coors Field, Denver (MLB #2 - Why do they score so many runs here?)

I think the highest-scoring MLB game I ever went to was when I went to a game in Denver between the Rockies and the Cardinals in 1993, the Rockies' first season, and it ended up 13-11. Last night's game was only 9-6, but that's still more runs than in the vast majority of major league games, and matches the reputation of games in Denver of being high-scoring.

It's not that it's a park with fences close to home plate in certain areas. In fact, Coors Field has the second-longest distance to the outfield wall down each of the foul lines, and the third longest to center field, and no park is bigger in all three of those. Rather, it's that it's easier to hit the ball. In their 30-year history, the Rockies have had nine different players who have led the league in batting average a total of 11 times, and no pitcher who has ever led the league in strikeouts. Incidentally, the 13-11 game I went to was played in the old Mile High Stadium, which had longer dimensions to right and center fields than any other stadium at the time.

So what's different about playing in Denver? The obvious thing is that it's the altitude -- Denver is famously the Mile High City, with an elevation over 5000 feet about sea level. Only two other MLB cities are above 1000 feet, Atlanta and Phoenix, and they're just barely over 1000, so Denver truly is extreme.

But why does altitude made a difference?

There's a website with a breakdown of how the Rockies did at home and on the road, by season, from 2003 on, which includes 19 full seasons, so I can start by seeing whether there really are more runs scored at Coors Field than elsewhere, or whether it's one of those things where once people expect something to be true (like strange things happening at Full Moon), they notice when it is true, but don't notice the counterexamples. This afternoon's game (which we didn't go to) was 3-2. Which is more representative?

Over the last 19 full seasons, the Rockies have indeed scored more runs at home than on the road, by about 50%, or nearly two runs per game. That's a lot, and confirms the reputation. But it turns out that the Rockies' pitchers have given up only half a run per game more at home than on the road. That also confirms the reputation, but brings up another question -- why is there so much more difference for Rockies hitters than for their pitchers? I wonder what happens to the performance of players to move to or from the Rockies between seasons.

But we still haven't figured out why batters do better (and pitchers worse) at Coors Field.

At higher altitude, the air is less dense, so there's less air resistance, which means a batted ball should travel farther. That sounds like there should be more home runs. In fact, the Rockies have hit 37% more home runs at home than away in those 19 seasons, a big number, but not as big as the 50% difference in scoring. Of course, if balls are flying farther, you could increase the size of the ballpark by enough that the number of homeruns would stay the same, but you'd still have more hits, because the fielders can't run any faster (and in fact, might run slower if their lungs aren't adapted to the lower oxygen level). So that's probably a part of it.

The density of the air doesn't just determine how far a ball will move, though. If there is more air resistance, the roughness of the stitches on a spinning ball will not have as much air to interact with, so a pitched ball will not curve as much. That could explain why the Rockies don't have pitchers who lead the league in strikeouts. I've long thought that a pitcher who relies more on changing the speed of his pitches and locating them well would do better in Coors Field than one who relies on movement of the ball. But I found out something interesting in that year-by-year data -- Rockies pitchers get almost the same number of strikeouts at home as on the road (2.5% more at home, which is not statistically significant). So I think the lack of strikeout kings on the Rockies pitching staff is more likely related to the fact that pitchers generally don't want to pitch there, so the Rockies can't get the best, than to any field effects. Or the Rockies may not be as good at selecting good pitchers in the draft of amateurs.

Incidentally, one early suggestion was that the difference is scoring was somehow related to the fact that Denver was also (at the time) the least humid MLB city, so the balls would dry out and, because they are lighter, could by hit farther. Starting in 2002, the balls for use at Coors Field have been stored in a humidor to reduce that difference. Even though the rest of MLB followed suit by 2022, I'm not sure how much difference it makes, and there's clearly still a big difference. For some reason.

The game: 

After two innings, the Padres had three home runs, and led 6-0. At that point, it looked like a runaway in the making, but the Rockies kept coming back, and with two out in the ninth inning, the Rockies were only behind by three, and had two men on base and one of their best hitters batting. Unfortunately for them, he grounded out, but at least it got close. Early in the game, Kerry said she thought that the Padres were going to be shaming anyone who didn't hit a home run -- they ended up with one each by five players, more than half their batting order. So the Padres won the battle of the two last place teams (in the five-team division), 9-6. 

It's ironic that the Padres are in next-to-last. Of the 30 MLB teams, only the two New York teams have higher payrolls, so Padres' is the highest in the division, nearly twice that of the Rockies, and more than twice that of the first-place Diamondbacks. I've always considered it nearly a duty to cheer against any team that spends that much money.