Tuesday, April 21, 2009

New Yankee Stadium Home Runs Not Necessarily Related to Weather

Yesterday AccuWeather via their blog put forth a hypothesis that the well documented increase in home runs at the new Yankee Stadium was due to a change in the stadium’s shape, allowing for west winds to enter and exit the stadium at a high speed and the proper angle to turn lazy fly balls into home runs. More specifically:

The wind on Saturday during the Yankees' 22-4 loss against the Cleveland Indians was mostly from the west at 15-20 mph. Given the layout of the stadium, the wind could have had an effect on fly balls in right field. Six home runs were hit by the Indians in the second inning alone.

Although the field dimensions of the new stadium are exactly that of the old stadium, the shell of the new stadium is shaped differently. AccuWeather.com meteorologists also estimate that the angle of the seating tiers in the new stadium could have a different effect on wind motion across the field.


Note the lack of scientific explanation for the statements in the article. Notice how many times words like mostly, could, estimate are used in the paragraphs. No modeling, or observational studies were used. Let me translate that for you into plain English, “hey we watched the game on Fox on Saturday and it sure looked like the wind was blowing the ball hard, maybe it’s the new stadium?” Look it seems like a reasonable hypothesis and all, especially watching some of those pop flies end up as home runs on Saturday, but it’s just a theory and the accuweather story struck me as being less science and more guessing. I was frustrated that a weather company would present this theory with only one games worth of wind data as as motivating observation.

So I wanted to test their theory with a bit of weather data to see if it holds any water. The methods are explained below and the study includes only six games the four versus the Indians this past weekend and two exhibition games versus the Cubs in early April. The chart shows the number of home runs hit each game, the mean direction of the wind and the wind speed. First note, only three of the six games hosted at Yankee Stadium so far had a west wind. So three of the games played so far had winds not out of the west, and often out of the opposite direction (east), which would by the accuweather theory suppress home runs. In each of these games where the wind was not out of the west, 3 home runs were hit.


Table 1. The above table shows the average wind direction, and speed for games at Yankee Stadium so far in 2009. See the methods section below for details.

During games with a west wind, 8, 6 and 5 home runs were hit, each a significant amount of home runs for a MLB game. But might these home runs be due to the players involved in the game and not the weather? I’m not a saberatician so excuse my clumsy attempt to convince you that there is just as good a chance that the HR’s were due to good offences hitting against struggling pitching as there is a chance that the wind was directly responsible for the home runs. Cleveland lead the American League in runs scored after the all-star break last year and is #2 in runs scored in this young season. During the west wind games this high powered offense was coupled with some exceptionally poor pitching. Of those three games with a west wind, two of them were started by Chien Ming Wang who has for a lack of a better word been awful both at Yankee Stadium and away so far this year. Other pitchers starting in these high home run games were Fausto Carmona (5.85 ERA in 2008, 7.87 ERA in 2009) served up 4 HR, Anthony Reyes (5.73 ERA in 2009, was lights out in second half of 2009) served up 3 HR while Joba Chamberlain (5.60 ERA in 2009 and 2.60 ERA in 2008 and arguably the best pitcher of the crew) only allowed 1 HR. Relievers who served up home runs include minor league pitcher Anthony Claggett who appeared to be overmatched, Jose Veras, Edward Ramirez, Zack Jackson and Jenson Lewis whos ERA’s range from 5.79 to 43.20 this year. Johan Santana, Tim Lincecum, Brandon Webb and Mariano Rivera these pitchers are not.

It’s too early to draw any conclusions from the weather data presented above. But it’s clear that a number of factors not related to the weather may have resulted in the home run deluge, and we can’t say for sure if the west wind is the cause of the HR deluge:

  • The accuweather hypothesis appears to be at best an untested guess, not based on modeling studies or scientific observation.

  • Winds have been equally out of the west as other directions, thus they can’t directly explain the deluge of runs and home runs scored over the weekend.

  • More home runs have been hit when there is a west wind at Yankee Stadium than when the wind has been from the east or south.

  • In the games with west winds the pitching has been poor, pitched either by pitchers who do not have demonstrated long term records of being above league average or are who are clearly struggling so far this season.

  • Cleveland and the Yankees are amongst the two best offensive teams in the American League

  • At this point there is not sufficient data to prove whether or not wind direction is statistically tied to home runs.


As Peter Abraham pointed out in his blog today, it’s too early to rush to judgment, the Yankees and opponents hit 20 HR in a four game series last year as well! It’s a neat theory to tie wind direction to HR production, but I think it’s irresponsible for accuweather to claim that the west wind is leading to these home runs. We’ll have to see what the numbers bare out this summer, and draw conclusions after a sufficient sample size has been drawn.

Methods. I calculated the mean wind direction, wind speed and air temperature at LaGuardia Airport from raw METAR code taken from the Plymouth State Weather Data Archive. LaGuardia Aiport was chosen to represent conditions in the Bronx due to the well documented problems with the Central Park observation site. The averages were calculated for the hours of the game, based on data taken from box scores, except during the exhibition games vs. the Cubs where length was estimated to be 4 hours.


Table 2. As per table 1, but includes standard deviation and temperature data as well.

10 comments:

John Carroll said...

good analysis, owen, but it is curious that more home runs were hit in each game when there was a west wind... old yankee stadium averaged 1.98 home runs per game last season, this season, so far, they are averaging 4.67... yes its only 6 games, but there is clearly something there... yankee stadium always had a short porch in right field, but anyone watching the games over the weekend, in particular on saturday, would have seen balls that should have been can of corn fly balls make it over the fence... if you observed the fielders tracking the balls, it was clear they also thought these fly balls should have been easily caught... also, if you look at the small sample size (3 games with west wind, 3 without) the results are almost significantly different (p=0.063)... that's not significant but with a larger sample size it could swing either way... while i agree that the accuweather report didn't have 'science,' keep in mind how many 'science' articles you might read in a paper or on a blog that don't show the science... this is for joe public, which lets face it, doesn't necessarily get actual science... i don't think the wind theory is without merit, and the data you give suggests it might not be... the indians are only #2 in scoring AFTER the 4 game set at yankee stadium, and while you certainly have some no doubt shots that go out regardless of winds, i am very nervous that what happened over the weekend is going to be more the norm than an anomaly...

Maggleton said...

For those of us who don't know the stadium, which way does the diamond face? Also of interest would be the direction of the homeruns. I don't know baseball that well, but I can imagine that one side or the other is favored for hitting homeruns, not to mention the probably difference in the distance to the outfield walls. Of course if you really wanted to go into it, you could use video of the games to calculate the trajectory of each homerun in still air and then compare that to where it actually landed and the wind strength at that moment. Lets see some physics here. :-)

Owen said...

John Carroll: You are right, at it's simplest we see more home runs so far with a west wind. I think I acknowledged that during Saturday's game it sure looked like pop flies were carrying out further. But the season is young, and the pitching on those days with a west wind has been not particularly impressive. I think accuweather mis-represented the wind conditions. They say that you need west winds in excess of 10 mph to generate the effect they are hypothesizing, yet that has only occurred in 1 of 4 major league games.

Maggs: The stadium layout, best I can tell via google maps is west (home plate) to east (right field). A lot of the home runs have been hit to right field, along the direction of a west wind, but a fair number were hit to left field as well (which would be a south wind). As per trajectory analysis you'd need wind observations inside of the stadium -- I'd bet money that the wind shifts in a spiral to some extent, so we can't just assume a west wind all the way to the field level.

John Carroll said...

oh no, i agree its early, but like you said, you watched the game... theres got to be something to that wind theory? and its like the scientific process, make an observation (yankees home games have a shitton of homeruns), formulate a hypothesis (as accuweather did, that the wind field created by the new yankee stadium more squat design is conducive to home runs, especially during west winds), test hypothesis (which you have started to do, but clearly more data needs to be generated) and formulate a conclusion or run more tests... i guess i find nothing wrong with their theory...

ccsuwxman said...

Owen:

I agree that there isn't enough data to support Accu-Weather's conclusion. What I pointed out on Pete Abe's blog is the construction of the Stadium itself, and how that may be responsible.

The old Stadium had concrete exterior walls with no windows or openings for wind to enter the park. The new Stadium, on the other hand, has open exterior walls, with high arches above the interior concourses through which the wind can blow. This makes it easy for a "wind tunnel" effect to develop, especially when the winds are from the west. Southerly winds will not produce this effect yet, as long as the old Stadium remains standing. It would be interesting to see if fly balls to center field begin travelling farther once the old Stadium is demolished.

Owen said...

Steve: I think you have a great point. The wind going into the stadium will be completely different after Yankee Stadium is torn down next door.

It's my plan to re-visit the data at the all star game and again after the season is over and see what drops out. Will have to do a pre vs. post demolition survey.

I think that the new stadium being open, as opposed to the old stadium being closed could certainly be a component of the wind tunnel effect, and as you note it was not included in the accuweather post.

Charles Ranhofer said...

I don't know if using LGA works. I was looking at the NCDC database, and LGA has a lot of mean N to E wind months during the late spring and summer, which doesn't make much sense at all based upon the typical synoptic pattern. My guess is that LGA gets a Sound-breeze, and that may make it a poor proxy for the Yankee Stadium wind (albeit an excellent one for Shea). I was at the game of Friday, and the wind was absolutely, 100% westerly

The question becomes: what is the proper station to use to identify the Yankee Stadium wind direction? If CPK is ruled out because the data is ratty, do we use EWR? White Plains? We can't use JFK b/c that will have a S/SE seabreeze bias.

-LDEO MA '07

ccsuwxman said...

Closest weather station to Yankee Stadium is TEB (Teterboro Airport). That would probably have similar wind conditions.

But as I posted earlier, until the old Stadium is torn down, all bets on exactly how the wind blows through the new Stadium are off.

Owen said...

Charles: I had not considered sea breeze interactions at LGA. I know many of the weather observers there and I'll get their opinion on this before repeating this experiment at the all-star game. My guess is that winds will not be strong enough during any sea breeze event that it would affect fly balls anyway. On days where there are strong west winds the sea breeze will be eroded.

It will be worth a look to compare observations at LGA, HPN and TEB.

Charles Ranhofer said...

Owen,

I think the seabreeze factor will be tremendously important. See
RC Gilliam et al., Metropolitan-scale Transport and Dispersion from the New York World Trade Center Following September 11, 2001. Part I: An Evaluation of the CALMET Meteorological Model
and citations therein.