Going Deep: Your (Ballpark) Is as Cold as Ice

Do you have a player who's struggling early this fantasy season? Fret not: Daniel Port may have the key to understanding why!

Baseball and summer, two words that are pretty much ubiquitous in America lore. Writers much more talented than me wax fancifully about young men and women sprinting through green, freshly cut grass while being warmed by beaming sunlight so bright you have to squint just to see from the outfield. It’s an image that sums up the best things about baseball in one beautiful picture.

The thing is: Baseball is a seven-month season. It takes a month-and-a-half to nearly two months before that idyllic scene comes to fruition. Until then? It can be very cold. There can be snow. April is the month that is known for raining all the time. Then it plows through that gorgeous summer weather before it tailspins back into the cold, crisp fall weather. Nearly half the season is played in cool to cold weather, and for one reason or another, we never seem to talk about it. Tune into most any early-April game broadcast and you’ll likely hear commentary about how cold it is and how that cold weather negatively affects the player’s performance. There’s a ton of scientific study that has been done on how the weather of a given day can have a massive impact on everything from how the player’s body performs to how a ball spins to how far a ball goes when it is hit. If there’s one thing that all these studies agree on, though? Weather below about 50 degrees Fahrenheit has a negative impact on how well a baseball player performs.

What does this have to do with fantasy baseball? We are in what I consider the most difficult part of the fantasy season. WE DON’T KNOW ANYTHING ABOUT ANYTHING. Sorry, it stresses me out sometimes. We don’t have anywhere near enough data to start determining what is real and what is not, but there are waiver wire moves that you need to make, injuries to worry about, and perhaps most importantly for our topic, slow starts that need to be dealt with. Focusing on the idea of slow starts, what are you supposed to do? Is that slump the start of a new normal, requiring you to head to the wire and fix the situation before it’s too late? Could it be simply a blip in the radar, a simple cold stretch that we would easily dismiss if it happened in the middle of the season? It’s really hard to know at this point. I ask again, what can you do? You can add context.

There are many different levels of context we can factor in. Is there some outlier BABIP action going on? Have they faced a large number of elite pitchers or defenses through their first six games? Did they get adequate playing time in spring training? What we’re asking here is: Can we derive any context from the early-season cold weather that might help explain any slow starts through the first six games of the season?

Let’s see what we can find. First, here is the average temperature over the last five years for every major city that has an MLB team and the average temperature through the first five days of April this year.

Note that you can hover over the data points on that chart and see the exact numbers for both lines. It actually breaks down pretty cleanly, with 30% of the league’s teams having an average home temperature over 60 degrees, 40% of the teams hovering between 60 degrees and 50 degrees, and the remaining 30% of teams forming a nice bookend by having an average home park temperature of below 50 degrees. This is represented by the blue line in the graph.

Take a look, though, at the red line. This represents the average temperature in that city for the five days we’ve had in April. With one exception (way to ruin everything, Seattle), almost every city is experiencing temperatures below their five-year average for April. Some of them are significantly colder. Pittsburgh is nearly 10 degrees colder on average than its five-year mark! Baltimore, Washington, and Atlanta are all nearly eight degrees colder than the five-year average. It is obviously going to get warmer as April moves toward March, but so far it’s been pretty darn cold. Through six games, we still see 30% of the teams have an average April temp above 60 degrees. But now only 20% of clubs are seeing temperatures between 50 and 60 degrees, which leaves a whopping 50% of teams playing in average temperatures below 50 degrees. That has a huge impact on performance.

The question is how much does it affect performance? Let’s ask science.



Sorry, I can’t help myself. I also apologize to all the Mr. Wizard fans, but this article is a Bill Nye household so long as I’m in charge around here. As I mentioned in the introduction, there have been quite a few studies done on the relationship between temperature and baseball. If I were to sum up each one, they would all pretty much agree that warm temperatures are good for performance and cold temperatures are very, very bad for player performance. Let’s get more in depth, though. Temperature can change a baseball game dramatically.

The first place we see temperature’s impact is in the baseball itself. The physical properties of the ball will change with the surrounding temperature. This might not seem like a big deal, but in a sport where we debate the size of the stitching on the ball (it turns out it makes a huge difference on how much drag there is on it) even the slightest difference can completely alter the game.

A baseball’s performance is measured using what is called the Coefficient of Restitution, or COR. For our purposes, this is essentially a measurement of how fast the ball comes off the bat relative to how hard it was thrown. MLB tightly regulates the COR for its baseballs. In this fascinating study conducted at the University of Massachusetts Baseball Research Center, they propelled balls at four different temperatures—120 degrees Fahrenheit (the study supposed this would be the equivalent of a ball being left out in the sun for an extended period), 70 degrees Fahrenheit (room temperature), 40 degrees Fahrenheit (to simulate night-game/cold day-game temperatures), and finally 20 degrees Fahrenheit (cold night games).

They then took those balls and fired them at a wood block at 60 mph and 100 mph to simulate striking a bat. Using photogates, they measured the COR for each baseball fired. They found that the balls fired at 100 mph weren’t affected until the temperature got below 40 degrees, and then the COR value plummets about 3%. This implies that when you play games at temperatures below 40 degrees balls thrown at high velocities are going to come off the bat came at much lower velocities. This would have a huge impact on the batted-ball results. Where this gets really interesting, though, is when they measured the baseballs thrown at 60 mph. Here’s a chart of the results.

Temp in Fahrenheit COR % lost from 120 Deg. Fahrenheit
120 0%
75 1.8%
40 2.3%
20 4.7%

There’s a lot more going on here. Where high-velocity pitches are largely affected only by extremely cold temperatures, we see an immediate effect as velocity drops. This makes some sense, as you don’t need to supply as much of the energy needed to leverage the ball a large distance. The pitch is supplying most of the energy; you’re just redirecting it and adding to it. On the other hand, when the pitch has a lower velocity, the batter now has to supply the energy to hit the ball that same distance. If the temperature reduces the COR of the ball, you have to hit the ball even harder. This article sums it up perfectly. Say it is a hot summer day and you hit a 60 mph curveball 400 feet for a home run. Now let’s say it’s 40 degrees outside (it’s been below that pretty much every day in Toronto this season) in April and you hit the same ball; you would lose 2.3% of that distance, or 9.2 feet! In some parks, that’s a flyout at the warning track instead of a home run, so it’s pretty easy to see the huge impact that temperature has on the ball, especially these days, when we’re seeing more and more breaking balls.

Another study I wanted to mention was done in 1995 that showed that reaction time is significantly slowed when your body temperature drops 0.5 degrees Celsius (0.9 degrees Fahrenheit). Baseball is entirely dependent on reaction time and fast-twitch body movement. So while it is unlikely with all your clothing and running around that your body temp would drop that much, even the slightest effect on your ability to react could be catastrophic to performance. You’re trying to hit a ball that’s traveling somewhere between 75 and 100 mph with crazy movement and you only have a few milliseconds to do so. There’s no such thing as a minute effect on your reaction time and your body’s ability to execute.

So we’ve seen the science. Now let’s take a look at the data and how this science affects league performance.


Sorry, Bill, but us baseball fans cannot live by science alone! I took a look at several stats over the last five years and broke them down by month.

You can clearly see that across the board the numbers rise from the cold months of April and May to level off throughout the middle months of summer only—then drop back down as things cool off again temperature-wise in the fall. Now it’s important to touch briefly on two different concepts that factor in heavily in the statistics world: correlation versus causation. Correlation implies that we can draw a very confident connection between a cause and a result. In this case, we can’t completely do so. There seems to be pretty heavy evidence that the weather has a huge effect on hitting, and the statistical trends absolutely support that, but we can’t prove beyond a shadow of a doubt that this is the only reason for these numbers.

Is spring training not long enough? Are the numbers watered down by young players trying to hold down spots they eventually lose? Does the same thing happen at the end of the year after rosters expand? Does it simply mean it takes longer for hitters to get into the season, and do they wear down more over the course of the campaign?

We don’t know any of them for sure. In all likelihood, it’s a combination of all these factors, but the numbers, trends, and science lean toward the weather as being a large factor in these depressed numbers. This is called a correlation. There is a strong connection between the temperature and hitter production, but we can’t say with 100% confidence that this is the case. My goal more or less here is to add one more piece to the puzzle, or in this case, one more potential explanation as to why a hitter may struggle early in the year.

My next goal with these numbers is to see if there is perhaps a different kind of batting split that we can use to help us when analyzing hitters. Once I start narrowing that down I will, of course, publish what I find and examine some hitters it applies to. In the meantime, when you have a player who might be fly-ball dependent or relies heavily on exit velocity, take a look at their game log. See how often they played in cold weather, and if they struggled in those games, that might be a good sign that their struggles could be weather-related as opposed to being skill-related. Same for their exit velocity. If there is a large drop in their exit velocity so far this season and they played in cold weather, it is likely that their exit velocity could be being held back by the ball’s actual temperature and its reduced COR.

Oftentimes during this part of the season we are forced to make a lot of gut decisions on early results in a very small sample size. Hopefully, information like this might help us make more informed decisions and not overreactions (or underreactions) that we will regret later in the season.

(Photo by Russell Lansford/Icon Sportswire)

Daniel Port

Daniel is a Fantasy Baseball writer, Brewer, and Theatrical Technician, located in Denver, Colorado. A lifelong fan of baseball and the Cleveland Indians since before Albert Belle tried to murder Fernando Vina, he used to tell his Mom he loved her using Sammy Sosa's home run salute, has a perfectly reasonable amount of love for Joey Votto and believes everything in life should be announced using bat flips. If you want to talk baseball, beer, or really anything at all you can find him on twitter at @DanielJPort !

One response to “Going Deep: Your (Ballpark) Is as Cold as Ice”

  1. David Chung says:

    I enjoyed reading your well-written article. I’ve been interested in the relationship between temperature and sports for a long time—my grade school science project showed how temperature affects the elasticity (bounce) of tennis balls.
    It does seem like April has been colder this year, but I wonder what your first graph would look like if the first five days of the current month had been plotted against the same first five days of April, and not April averages. Secondly, I’m sure you had just forgotten that games in Toronto are played in the Rogers Centre, who’s indoor facility is temepature-controlled.

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