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Published in · 6 min read · Mar 6, 2023
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On May 28th, 2021 Cubs outfielder Patrick Wisdom crushed a Sean Doolittle fastball that was destined for the left field bleachers. If you heard the announcers’ or the crowd’s live reaction, you didn’t need Statcast to tell you that balls that leave the bat at 103 mph with a 34 degree launch angle typically travel 400 feet. Cubs’ broadcaster Jon Sciambi went into his home run call: “That one drilled, left field! This one back and…”. Meanwhile, the Reds’ broadcast had a more succinct immediate reaction: “Oh boy.” Fans in the 12th row of the bleachers jumped to their feet and stretched out their arms to make a play on the ball.
Then, suddenly, the mood shifted. Sciambi continued, “Oh man”, having realized that Reds’ left fielder Jesse Winker was settling under the ball, not in the bleachers but just one step onto the warning track. Reds play-by-play broadcaster Tommy Thrall elaborated, “The wind is going to help out the Reds here. That ball was crushed!”
Thrall correctly pinpointed the culprit: the wind, or the weather more broadly. Sensors and advanced modeling from Weather Applied Metrics (WAM) tell us that the wind cost Wisdom 40 feet on the would-be home run on this blustery day at Wrigley Field in 2021.
After testing the technology at five parks in 2022, MLB and WAM will be providing weather data and insights across all 30 ballparks in 2023.
Park sizes, orientations, shape, and weather can be considered as a group of factors in concept as a park factor. The park-factor ingredient that has historically been most difficult to characterize is wind.
Wind at a ballpark has to negotiate large structures that surround the field. As a result, wind on-field doesn’t match what the flags are showing. The figure below illustrates how a large barrier creates a wind shadow. The height (X) and range (Y) of the wind shadow are roughly on the order of magnitude of the height of the barrier.
In practice, that means, especially for large ballparks, the wind that affects ball trajectories doesn’t necessarily match the prevailing wind conditions. As a result, pitchers don’t often pitch into significant headwinds and hits can be pushed in different directions depending on where they are hit and the shape of the stadium.
Starting in 2023 MLB will be using Weather Applied Metrics (WAM) to quantify the impact of wind and weather effects at ballparks league wide. To do this accurately, WAM needs a higher resolution of wind and weather data than is practical using discrete weather sensors. They accomplish this using Computational Fluid Dynamic (CFD) modeling. The WAM CFD modeling process uses accurate 3D geospatial data to calculate a wind-field solution which uniquely matches the park’s boundary conditions and the prevailing weather conditions measured over the stadium. WAM exhaustively computes CFD solution sets in advance so the WAM workflow can react in real time to changes in weather conditions. The image below shows a vector wind-field solution for a ballpark where swirling winds change magnitude and direction depending on location inside the park.
Along with the wind solution from their CFD model, Weather Applied Metrics uses Statcast tracking data to calculate the deviation for a hit trajectory compared to an identical hit launched in calm conditions or in an indoor environment. The “calm” deviation isolates only the wind impact on the hit, but the “indoor” deviation adjusts for all weather conditions including the elevation of the ballpark. A “calm” trajectory deviation is shown below for Matt Olson’s grand slam from April 20th, 2021.
In a similar way, the weather impact on pitch location can be calculated. Pitch deviations are typically much smaller in magnitude than hit deviations because trajectories are shorter and closer to the ground. However, in parks with consistent wind trends, pitch velocity and movement can experience slight biases related to ballpark, season, and time of day.
In addition to calculating weather impact on past events, WAM can also forecast weather impact for games yet to be played. WAM forecasts use a generic home run trajectory to calculate the general expected deviation given the forecasted weather conditions for a given game. For example, the graphic below shows the change in distance (number) and deviation direction (arrow) for a generic home run trajectory.
A collective data set from WAM can help answer the following questions:
- Which parks have significant wind bias that affects pitch dynamics?
- In what parks does wind prevent the most home runs?
- Which players would benefit the most by moving to a neutral venue?
Given that WAM technology has been installed in a subset of MLB parks, we can answer another interesting question: How much can wind affect a hit trajectory?
Wrigley Field has interesting wind effects due to its proximity to Lake Michigan, but also because it’s an older, smaller park surrounded by structures that condense flow. Wrigley wind was evident on this Patrick Wisdom fly-out that was easily caught by the left fielder. Jon Sciambi’s play-by-play call reveals the story. This pitch was struck well and started on what seemed to be a home run trajectory.
Statcast measured an exit speed of 103 mph and a launch angle of 34 degrees. Off the bat, Sciambi and Wisdom may have thought this was a home run. But this hit died on the warning track. Luckily, in this case we had WAM data and we can see how much wind affected the distance.
To give some context, we can check Statcast hit data on balls hit this hard, at this launch angle. The histogram below shows the wide variety of distance outcomes that have been tracked since 2020. You can also see this Pat Wisdom flyout has the second smallest distance of all such hits. Most balls hit this hard have traveled around 400ft, but this hit only made it to 338 ft.
What causes this hit to be a distance outlier is the wind impact. WAM used the output of the CFD wind model to calculate the wind impact throughout the trajectory. The result was found to be a 40-ft reduction in distance compared to the same hit in calm conditions. The difference in landing locations is shown below.
How much can wind affect a trajectory? As this example shows, wind can knock a hit back 40 ft. In this case it was the difference between a home run 9 rows back and an easy F7 on the warning track.
In cases where the hit apex is extremely high, WAM analysis has shown that the change in landing location due to wind can approach 100 ft in the most severe conditions. When weather becomes part of the story of baseball, insights from Weather Applied Metrics can be found on your team’s broadcast during the 2023 MLB season.
