Analysis of the new dimensions of Kauffman Stadium

Yesterday the Royals made a big announcement. Kauffman Stadium, long one of the most cavernous venues in the majors, will be a little less warehouse-like this year. The walls move about nine or ten feet all along the line, and also become shorter by a foot and a half. That’s a meaningful change for a stadium where home runs are generally disappearing. How massive? Time to turn on the old computer and find out.

I put the new dimensions from the Kansas City press release into an equation that describes a rough arc. I placed those points on a cubic spline so it would look more like the real stadium, with the pinched corners. I’ve also made a few approximations; For example, the wall moves to a height of 8 feet ‘in most places’, so I just applied that across the board. I also modeled the old dimensions in the same way. In this way I had two different virtual walls built to compare some batted ball data.

It is striking that my approach is not a perfect replica of the stadium. I don’t have a millimeter-scale, or even meter-scale, map of the place. I can’t account for outfielders robbing home runs, which is sure to happen more often at the dropped walls, though it’s still pretty rare overall. But by running it through both the old and new wall dimensions, I think this inevitable error can be minimized. It’s pretty clear that balls that were home runs with the old outfield parameters will suddenly no longer be home runs with the new ones, so what we’re looking for is the difference, assuming my approximation is close enough to reality. And it is: my models say that over the last three years, 205, 162 and 159 batted balls in Kansas City, respectively, should have turned into home runs. In reality it was 186, 147 and 151.

In other words, my estimates are a bit high, but they are very consistent. A visual inspection of the misclassified batted balls usually consists of a pile of extra base hits off the wall, a few explosions from an odd angle that fool my trajectory-smoothing model, and a few jumping catches. Any of these will certainly turn into homers with the new dimensions. As long as we’re just using this model to look at change, I’m very comfortable with it, and in fact it may slightly underestimate the increase in home runs.

That said, let’s get to the data. I compared each batted ball from 2025 to both sets of wall coordinates and identified 43 new home runs in the new configuration:

I ran the same test for each year for which we have Statcast data. After all, because the walls have already been built virtually, I can throw a lot of different batted balls against them without much effort. The average increase in home runs over the past 10 years (excluding the shortened 2020 season, a sentence I’ll probably have to keep writing forever, like Sisyphus) was 51 per season. That’s a significant increase, and with nine out of ten readings between 40 and 60 (2023 had a 70 homer increase in the most energy-happy year according to Kauffman data), I’m pretty confident in the size of the effect.

What types of batted balls turned into home runs? The most valuable one you can imagine, actually. Kauffman does enormous. Most of the 43 batted balls I classified as in play in 2025, but home runs in 2026, landed safely for hits, even with the old dimensions. They had an average wOBA of .943, with a .700 BABIP. They were actually rockets; balls are hit at ideal home run angles, liners and fly balls are shot over the heads of outfielders with no chance of reaching them, but are held by the gigantic park. So 43 new home runs isn’t 43 more hits – it’s more like 43 new home runs, 13 fewer outs, and 30 fewer doubles and triples.

Want to see where the new homers would land? Well, everywhere:

The reason none of the dots are exactly on the new wall is that you need to clean it up, and the distances I’m using are projected landing points. But you get the idea; pull the walls in everywhere other than center, and you get a ton more home runs anywhere outside of center. The few scattered dots in the center are the strange beneficiaries of the lower walls.

What will this do to increase the score? I can take a guess, but it will still only be a guess until we see real games in the new dimensions. For example, trade in 50 new homers (a nice round number that’s close to the average increase from above), swap out the total mix of doubles, outs, and triples they “used to be,” and you get a total run score increase of 57.2 runs over 81 home games. Of course, that applies to both teams, as I used every batted ball to increase the sample size. That’s an extra .35 runs per team per match, still a meaningful boost. Even if we scale that back a bit on the assumption that fielders will do better with the remaining balls in play because they have to cover a smaller area, that’s still a huge improvement.

While Kauffman has long been one of the worst ballparks in baseball in terms of home runs, it wasn’t an offensive wasteland. Park factors generally put it around neutral. Last season was actually the first year since 2019 in which the Royals scored more points on the road than at home. That doesn’t mean it’s hugely attack-friendly – ​​there is home advantage – but a number of different approaches to the park factor independently determine the stadium as roughly average. Add 0.3 runs to each team every match, or even 0.25 if you really think BABIP will lose a ton thanks to the smaller size, and we’re talking one of the friendlier stadiums in the league in terms of attack.

Of course, the actual effect on scoring will be more nuanced and seasonal than my broad reclassification of batted balls. Dr. Daniel Mack, the team’s vice president of research, explained Some of the additional factors the team considered when making the change: “(Senior Analyst) Alan (Kohler) and I started tearing it down. What is the effect of the walls? What is the effect of the height? What is the effect of the temperature and the wind? We’re trying to figure out how to take all these effects into account and balance them.” Kauffman doesn’t play the same thing all year round; Kansas City experiences huge variations in weather throughout the year, with significantly changing drag and wind patterns. The stadium plays differently in April than it does in July, something I didn’t even try to model in my quick shot. But averaged over the year, I think the increase in scoring is at least in the range of what will happen, with enough home runs being added to more than take the sting out of the lost doubles.

I may not have the exact week-to-week fluctuations, but the data is still good enough to make some predictions. I first noted which players would have seen the biggest increase in Kauffman home runs with the new dimensions. Michael GarciaBy this estimate, 2025 batted balls with the new walls would have yielded an additional five home runs, while Jonathan India would also see his homer total increase by five. Salvador Perez’s would increase by four, with Vinnie Pasquantino’s and Bobby Witt Jr.increases by three each.

We can go back even further. Here is a ranking of career homers “won” in the alternate universe where Kauffman always had smaller dimensions:

And of course a ranking of the pitchers who would have suffered the most. I’m shocked Yordano Ventura is there with only two seasons of data, but he happened to give up a lot of not-quite-homers in those two years:

While the magnitude may be uncertain, the direction of change is clear. The new dimensions of the stadium will produce significantly more home runs. That’s very much on purpose. Like Mack detailed According to Jeff Passan, the purpose of this size change was to produce a league-average run value for fly balls in the park. Although Kauffman generally plays as a more or less neutral park, home runs are greatly suppressed while doubles and triples are handled.

The value of flyball runs is historically low at Kaufmann because a disproportionate amount of that value comes from home runs, while the extra doubles and triples have undermined the value of line drives. That doesn’t reflect the incentives at every other stadium in the Majors, and this change addresses that head-on.

Well, a bit direct. The new dimensions certainly help balls fly. By my estimate, 24 fly balls that didn’t leave Kauffman in 2025 would have been home runs with the new walls. But 19 line drives that didn’t leave the park in 2025 would also have failed. To be fair, the line drives were much more productive than the fly balls with the old wall configuration, so the upgrade to the fly ball value is real. But line drives are also becoming increasingly valuable. And while the new dimensions will reduce the area outfielders need to defend, Kauffman will still boast significantly more outfield square footage than average, so the days of gappers and speed are hardly over.

Will Bobby Witt Jr. could hit a trillion home runs by 2026? Will the Royals become the new offense in KC with Patrick Mahomes on the shelf and the Chiefs in a short slump? We won’t know until they play the games. But Kauffman has always been more offensively friendly than his ample size suggests, a kind of mini-Coors. Pull the walls in and we’re in for some fun brawling. I hope the Pasquatch did his cardio.