Jason Kipnis started spring training ablaze in 2018. Through 30 plate appearances, Kipnis has belted six homers and earned a .500/.517/1.250 slash line.
Most of Kipnis’ torrid start can be attributed to his changed off season regimen. According to Zack Meisel of The Athletic, Kipnis:
“…prepares sooner; he started throwing and hitting before Thanksgiving at Curtis Granderson’s indoor facility at the University of Illinois at Chicago. In the past, he held off on initiating his regimen until New Year’s.”
Mired in trad rumors most of the off season, Kipnis is slowly proving that the Indians made the right choice in not dealing him to another team.
Kipnis’ power surge has certainly been impressive. It begs this question, however: How much of his power is aided by the thin and (nearly) humidless air of Goodyear, Arizona?
The table below illustrates the simply delightful weather for both the Grapefruit and Cactus leagues. With the exception of relative humidity, the climates are remarkably similar in March.
| March Average Weather | |||||
| Location | Daily High Temp | Rain | Days With Rain | Humidity | Wind Speed |
| Pheonix | 77 | 1 inch | 4 | 38% | 6.4mph |
| Tampa | 76 | 3 inch | 7 | 71% | 8.3mph |
In 2016, Alan Nathan summarized the effect of air on a fly ball in “Going Deep on Goin’ Deep.” He stated that a ten degree increase in temperature would result in a 3.3-foot increase in distance for a typical fly ball, so the temperature variation between the leagues will make little difference.
The same can be said of the humidity, because a 50 percent increase only results in a 0.9-foot change in distance. According to David Kagan, a physics professor at CSU Chico:
“…the wind might make a bit of difference, because a five mph wind will change the distance by about 19 feet. So, the difference here would result in about eight feet. However, the direction of the wind could be in, out, or across the field so, the wind-related variation from Grapefruit to Cactus is something of a wild card.”
There must be something funny about the way the air across Florida interacts with the ball compared to Phoenix because the ballparks are different. Below is a table indicating the distance to center field for each park in each league, courtesy of Ballparks of Baseball:
| Cactus League | CF (ft) | Grapefruit League | CF (ft) |
|---|---|---|---|
| Camelback Ranch | 410 | Bill Hammond Stadium | 405 |
| Goodyear Ballpark | 410 | Bright House Field | 408 |
| Hohokam Stadium | 410 | Champion Stadium | 400 |
| Marysville Park | 400 | Charotte Sports Park | 402 |
| Peoria Stadium | 410 | Ed Smith Stadium | 400 |
| Salt River Fields | 410 | Florida Auto Stadium | 400 |
| Scottsdale Stadium | 430 | Jetblue Park | 410 |
| Sloan Park | 410 | Joker Marchant Stadium | 420 |
| Surprise Stadium | 400 | Lecom Park | 400 |
| Tempe Diablo Stadium | 420 | Roger Dean Stadium | 400 |
| Steinbrenner Field | 406 | ||
| Ballpark of Palm Beaches | 408 | ||
| Tradition Field | 410 | ||
| Average | 411 | Average | 405 |
The reason why Cactus League parks are on average larger than the Grapefruit League venues is because Phoenix is at an elevation of 1,124 feet, while Florida is a couple of decades away from being below sea level.
Nathan’s work tells us that fly balls should travel an extra six feet for every thousand feet of elevation. It is a lovely coincidence that this matches the difference in average center field distance between the two leagues.
One might therefore expect the number of homers in the two leagues to be roughly the same. Here are the numbers for 2018 spring training from mlb.com.
There are many more at-bats in the Cactus league, which is probably due to fewer rainy days, so one should expect more home-runs in Arizona even though there are 15 teams in each league. Overall, there are still 10 percent more homers per at-bat in Phoenix even with the larger stadiums. Here are a couple of possible explanations.
According to Kagan, there are a few explanations for this:
- This one year of data is just unusual for some reason.
- The wind blows out more often in Arizona than Florida.
- The pitching is also affected by the difference in the elevation.
He goes on to explain:
“As a physicist, the possible explanation that most interests me is the pitching question, so you’re stuck hearing about it. As we know from the mad scientists of baseball and their continuing evil experiment at Coors Field, not only does the mile-high air affect the flight of fly balls, it also limits the break on pitches. There should be a smaller, but nonetheless appreciable, drop in break due to the thinner air in Arizona compared to Florida.”
Corey Kluber throws a repertoire of a four-seam fastball, slider, sinker and cutter, according to data collected from Brooks Baseball. Using a model of the trajectory of the flight of a pitch and some data from Brooks baseball, Kagan calculated the change in position of each pitch at the plate due to the air of Phoenix.
The results for the change in horizontal position (∆x), the vertical position (∆z), and the total position change (∆r) are shown in the table below. Kagan developed the criteria:
| Pitch Type | x in. | z in. | r in. |
| Fastball | -0.12 | -0.64 | 0.66 |
| Slider | 0.05 | -0.40 | 0.40 |
| Sinker | 0.55 | -0.05 | 0.22 |
| Cutter | -0.02 | 0.42 | 0.42 |
According to Kagan:
“Since a four-seamer has mostly backspin, it will rise less in the thinner air of the Cactus League, which it does, as the 0.64-inch decrease in the height (∆z) shows. [Klubers]’s slider, unlike many, has substantial backspin as well, and it also rises less—0.40 inches in this case. His sinker, which has topspin causing it to drop, is also less effective in that it crosses the plate 0.42 inches higher in Phoenix.”
These differences are rather large. That is to say they are an appreciable fraction of the diameter of the bat, so they could account for batters’ extra power in the Cactus League. After all, if your fastball loses over six-tenths of an inch in hop, and your curve loses over four-tenths of an inch of drop, you’re going to have some trouble on the mound.
Of course, one could argue against this explanation by pointing out that elevation changes are a standard problem that big league pitchers solve every day (except in Denver). Excluding Coors Field, the average elevation of major league parks is 357 feet, and they vary from nine to 1,082 feet in elevation according to Kagan. Still, losing around half-an-inch of break can’t make a pitcher’s life very easy.
Kipnis’ power surge this spring isn’t all attributable to the rarefied Arizona air.
However, his homerun numbers may not be as impressive if they were still playing spring games in Winter Haven, Florida.
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