I’ve been investigating how the weather at the start of Colorado Rockies games at Coors Field affects run scoring and the Rockies’ winning percentage. In Part 1, I took a look at temperature and drew a few conclusions, including the observation that the Rockies tend to win more the warmer it gets. In this part, I will be looking at wind. Part 1 also has some helpful notes about the weather data and how I’m using it here.
Wind is difficult to capture and can vary quite a bit from game time readings. Additionally, the Coors Field readings from the anemometer at the top of the Rockpile might not affect field level conditions or affect balls differently depending on how high a batted ball goes (you can keep track of Coors Field weather here). Andrew Perpetua noted how the structure of a ballpark and various surrounding buildings can change wind’s influence. Ultimately, the best way to get an idea of what the wind is like is to look at a live box score or, during the game, look at the flags on top of the Rockpile. The affects of wind should be taken with a grain of salt.
The dataset includes 799 games (there is no information for 12 games) at Coors Field from the 2007 to 2016 seasons. All data courtesy of Retrosheet.*
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The chart below shows the average runs scored per game and the Rockies winning percentage based on wind direction. It is sorted in terms of highest run scoring environment (Total Runs Per Game) to lowest. In the chart below, I classified “Calm” as wind speed two mph or less. Everything else is three mph or more. I also translated wind directions to areas of the field to compass directions.
Game time wind speed can affect the runs scored at Coors Field. The highest run scoring environment is when the wind blows northeast out to right field at 12.0 runs per game, and the second highest runs per game occurs when the wind travels east, from left to right. In terms of compass directions, that means it’s likely to be a high scoring game if the wind is blowing northeast or east at game time. When the wind blows out to left field, the run scoring is about average for Coors Field. Unsurprisingly, the lowest scoring environment is when the wind blows south, from center field, with just 10.4 runs being scored per game. In general, if the wind is blowing out to center field or in from center, run scoring is suppressed.
Additionally, whether the Rockies win or lose also seems to be affected by which way the wind is blowing. The chart below breaks down the Rockies runs per game versus their opponents based on wind direction, sorted in descending order of winning percentage.
The Rockies tend to win more often than their overall .541 win percentage when the wind blows anywhere from north to east on the compass. The Rockies outscore their opponents the most, at an average of 1.1 runs per game, when the wind blows directly east, from left field to right field. However, if the wind is blowing in from either left, center or right, or if the wind is calm, the Rockies have no advantage in run scoring over their opponents.
Curiously, the Rockies outscore their opponents by 0.8 runs per game when the wind blows out to left field, but their .527 winning percentage is less than their overall .541 winning percentage. With 93 games in that particular grouping, there’d have to be a lot of blowout games in the Rockies favor to trade off the extra runs scored versus all those lost games.
The graph below is plotted in terms of wind direction based on how many runs the Rockies score versus their opponents in terms of wind direction. If there is a gap between the two lines, the Rockies are outscoring their opponents in that wind direction. The calm direction is omitted.
The chart below breaks up the overall run scoring based on wind conditions in terms of home runs per game and hits per game. The differences listed are a straight subtraction between the home rate percentage per plate appearance and the visitor rate per plate appearance. The greener a cell is, the better the Rockies have done than their opponents based on the game-time conditions.
It’s striking that the Rockies score about as often as their opponents when the wind is calm or the wind is blowing in. Though they still hit more home runs and generally get more hits than their opponents, the difference isn’t as significant as when the wind is blowing out.
As I mentioned earlier, though the Rockies tend to outscore the visitors if the wind is blowing out to left and have significantly increased hit and home run rates, the extra runs don’t result in an elevated winning percentage. I broke the run scoring down into multiple components, looking at individual types of hits, walk rates, even sacrifice flies to try to tease out the reasons. The chart below looks at some (but not all) of the overall rates. Cells highlighted green indicate the Rockies have better rates than their opponents, while red cells indicate their rates are worse. In terms of the percentage of strikeouts, a higher percentage means increased strikeouts and worse rates, colored in red.
In general, the Rockies tend to get on base more, get more base hits and hit for more home runs than their opponents at Coors Field, though they are a tick less than even in terms of doubles. All things being equal, if one team regularly has a higher OPS than an opposing team and scores more games than the opposing teams, they should win more games. Yet, there is no particular component advantage that opponents have when the wind blows out to left field that would suggest why they win more games than the Rockies. The Rockies even hold an edge in home run rate if the wind blows out to left field. However, it appears that when the wind blows out to left field at the start of the game, the Rockies plate discipline becomes worse, as their walk rate decreases and their strikeout rate goes up. But when the wind blows out to center or right, the Rockies tend to draw more walks than the opposition and they tend to win.
On the theory that plate discipline might be affected by the wind at game time, I took a bit of a leap and decided to compare the Rockies walk rate compared to their opponents with their winning percentage. The Rockies winning percentage increases as they draw more walks than their opponents. The solid line is the Rockies winning percentage plotted against the difference in walk rate between the Rockies and their opponents. The dotted line is the best fit line.
The correlation between the two variables is a statistically weak 0.392, but not insignificant. The advantages in the other components might make up for that diminished walk rate, but perhaps a swing for the fences mentality because the wind is blowing out to left might be hurting them in those close games. Nonetheless, when the wind blows out to left, the Rockies walk much less than their opponents, and they tend to lose.
Here are the major takeaways:
- The highest run scoring environment at Coors Field is when the wind blows out to right field at game time and the lowest is when the wind blows in from center field.
- If the wind is blowing north (To CF), northeast (To RF) or east (LF to RF) at game time, the Rockies tend to win at a much higher rate than their normal home field winning percentage. If the wind blows southwest (From RF) or there isn’t much wind, the Rockies tend to lose more often.
- The Rockies tend to outscore their opponents if the wind isn’t blowing in from left, center or right field, but their winning percentage doesn’t always increase.
- Walk rate seems to increase the Rockies chances of winning and both walk rate and strikeout rate seem to be affected by the weather.
Next up is the conclusion of this series which will put the wind and temperature data together for some additional insights. It will have more component level detail, which will be a factor to figuring out why the Colorado Rockies don’t do as well at Coors Field at certain temperatures and wind combinations.
*The information used here was obtained free of charge from and is copyrighted by Retrosheet. Interested parties may contact Retrosheet at 20 Sunset Rd., Newark, DE 19711.