Additionally, the interaction between outfield space and outfield wall height may also play a role, as could climate and, more specifically, weather so far this season. As mentioned, we don’t know for sure which parks added the humidor. Ultimately, the answer to why certain parks might have been more impacted by the new run environment than others is difficult to unpack. Exit velocity is not the only way to mitigate player-specific effects, but it is an important factor to keep in mind when thinking about park-specific home run rates. Without getting too deep into the mathematical details, some parks - like Oakland Coliseum and Busch Stadium - still had significantly large residuals, meaning that even after accounting for any exit velocity changes, the difference in home run rate was notable. To mitigate the effects of player-specific changes driving these shifts in home run rates, I built a simple model that incorporated a 2019–21 change in average exit velocity to the associated change in home run rate. Similar trends can be observed for other ballparks as well. The table is sorted by raw percentage difference, but the statistical tests incorporate sample size, which is why certain rows may have smaller differences but are still significant at a more extreme alpha level: 01 level, and parks highlighted in yellow experienced a significant change at the alpha =. I ran a difference in proportions test to compare the rates from both years parks highlighted in red experienced a significant change at the alpha =. ![]() (The r-squared between launch angle difference and home run rates was just 0.01.) Even still, after using a model to fit the change in home run rates of each ballpark to account for any exit velocity changes, there was quite a significant difference for certain parks that is more likely to be the result of non-player effects, like the baseball or the addition of a humidor.įirst, here are the raw home run rates for these types of fly balls for each ballpark from 2019 to ’21. I did attempt to examine the impacts, if any, of these exit velocity changes on home run rates, and there was a moderate correlation (r-squared of 0.28) that is important to keep in mind. The chart is sortable, so you are able to examine any changes in fly ball quality within this broader 95–109 mph exit velocity, less-than-30 degree launch angle group as you wish. This includes all fly balls hit between 95–109 mph and at a launch angle of less than 30 degrees in these parks by batters on both teams that played here during games played on or before May 31 in each year. (That is why I am comparing 2019 to ’21.) I also only included fly balls hit in games on or before May 31 to control for weather effects. To mitigate these effects, I only analyzed a specific slice of fly balls: those hit at an exit velocity at or above 95.0 mph, at an exit velocity below 110.0 mph, and at a launch angle below 30 degrees - the very fly balls most impacted by the new baseball in my prior analysis. It’s entirely possible that, between 2019 and ’21, a team added home run hitters to its lineup or acquired home run-adverse pitchers for its staff, or the opposite could also be true. We can only guess which parks now have them, but it is important to keep in mind that the ball is not the only difference.Īlso important to remember when looking at ballpark-level data: The players on the home team make a huge difference in determining home run rates. The Rockies, Diamondbacks, Mariners, Mets, and Red Sox already had humidors in their stadiums pre-2021, but which five teams are new to that list has yet to be disclosed. MLB reportedly added humidors to five stadiums for the 2021 season, bringing the total league-wide to 10. ![]() That allows us to understand better how park effects may have been altered to different degrees as a result of MLB’s switch to the new baseball.īut it’s not just the baseball that is contributing here. ![]() Though league-wide trends are certainly an interesting and informative way to see the effects of a new baseball on run scoring, it is also important to examine in which parks hitters are having a more difficult time getting the ball into the seats. There were a handful of outstanding questions that I still had, one of which was the impact of the new baseball on a ballpark-by-ballpark basis. In 2021, these events are now doubles and outs, with the increase in fly outs likely contributing (at least somewhat) to baseball’s diminished run environment overall. In 2019, these events were the wall scrapers that barely went out of the yard. ![]() The conclusion was pretty much exactly what you’d expect: A bouncier ball with more drag did reduce home runs, particularly among softer-hit balls at lower launch angles. At the beginning of May, I wrote two articles about the slightly-deadened baseball’s effect on league-wide home run rates.
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