By E.J. Fagan
September 8, 2023
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NOTE: The following comes from EJ Fagan's substack page and is shared with permission.
Please check out EJ's substack page for more great articles.
This article was first published on August 19, 2023.
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I’ve been curious about the weird Yankee underperformance in xwOBA since the season turned sour. Around the All Star Break, I noted that the Yankees might be falling into the trap zone of exit velocity, where at certain launch angles you get a better result by hitting the ball less hard. See this figure from Rob Arthur:
The above figure shows the expected run value of balls in play. I’d like to recreate it at some point, but for now I want to do something simpler. How much do batters benefit by on average hitting the ball harder?
I took all qualified batters during the 2022 and 2023 seasons and compared their wOBA and their average exit velocity. As expected, I found that batters who hit the ball harder tend to have higher wOBAs. That’s not a surprise. But, the relationship is complicated.
Below is a scatter plot. I’ve divided batters into two groups: those with an average exit velocity over 91 and those with one equal to or less than 91. You can see a much different slop (the lines) on exit velocity for both groups.
What does that mean? It means that launch speed has a non-linear relationship with wOBA. To repeat huge gains from more launch speed, you have to get past a certain point. Launch speed explains a lot less of the variation in wOBA when batters hit around 90 mph on average than when they hit 93+.
How big of a difference? More than double. Below is a plot of the coefficient on the relationship between exit velocity and launch speed. For each extra mph of launch speed for a batter who on average hits a batted ball less than 91 mph, they gain about 0.006 wOBA. For each extra mph for the batters who hit more than 91 mph, they can about 0.02 wOBA.
That’s a huge difference in effect size. If you can hit the ball really hard all the time, it makes sense to try and hit the ball even harder. A batter who on average hits 91.5 mph and increases it to 92.5 mph can expect to increase his wOBA by 20 points! Damn. But, a batter who hits 88.5 mph and increases it to 89.5 mph only expects to increase his wOBA by 6 points.
In both cases, you have to ask what the batter is sacrificing to increase their exit velocity by 1 mph. Are they hitting fewer line drives? Pulling the ball more? Striking out more? Are there alternative strategies that they might be able to take which could increase their wOBA by more than 6 points? There are real tradeoffs involved here.
To make matters worse, most Yankee hitters sit in that low returns to extra exit velocity danger zone:
Volpe’s launch speed really pops out to me. He’s capable of occasionally running into one, but is a pretty average MLB hitter as far as exit velocity. Maybe he shouldn’t be trying to hit the ball 105 mph so much? Instead, maybe he should be trying to hit more bloop singles and line drives, similar to how Rizzo and LeMahieu hit.
Compare the distribution of Volpe’s exit velocity to Rizzo’s in 2022:
Volpe actually hits more balls over 98ish mph than Rizzo.* Yet, 2022 Rizzo was a way better hitter, .352 wOBA vs .299. Some of the difference is that 2022 Rizzo hit the ball about 1 mph faster on average than Volpe, but we’ve seen that the difference only accounts for about 0.006 wOBA. Instead, we can see that Rizzo hits a lot more balls in that mid-90s exit velocity range, while Volpe hits more in the high-90s, low-100s. Rizzo also put a lot more balls in play (18% strikeout rate vs. Volpe’s 27%).
The tldr here is that it might make sense for some players to try really hard to hit the ball a little harder, but for others the returns are low. So low that it might be worth exploring some other strategy. Someone like Jake Bauers is probably in that spot where an extra mph really helps. Someone like Volpe probably isn’t.
*This figure understates the difference between the two a little bit. Rizzo had 100 more balls in play than Volpe.
