Saturday, December 23, 2023
Swing Speed: Arraez v Acuna
Acuna has a swing speed of 77.4 mph, one of the fastest in the league. Arraez has a swing speed of 63.8, one of the slowest in the league. When we limit each of their swings to their personal 90% fastest swings (meaning we drop their 10% slowest), here is how their distributions stack up (click to embiggen).
As you can see, their shapes are similar, but just shifted over by 13-14 mph. Notice that around 67-73 mph they overlap: Arraez at his fastest 20-25% of swings is Acuna at his 20-25% slowest of swings.
Now, look what happens when we show the run production by swing speed:
Arraez is overall -4 runs on swings. But at 67+, he is a healthy +7 runs (and naturally -11 runs below 67 mph). Acuna on the other hand is at his worst at under 76 mph, -6 runs, while he is a superlative +16 runs at 76+.
As you can see, Arraez at 67-73 and Acuna at 67-73 is totally different. Arraez at his top speed means he did everything he wanted to do, while Acuna at his low speed means that there's an indication of something going wrong. That's why you can't just look at swing speed on its own: it really needs to be evaluated based on that batter's swing distribution.
More to come...
Great data. And the contrast in outcomes in the overlapping range (67-73 mph) is very interesting. I wonder if that can be explained, at least in part, by the pitch count (and therefore, pitch type). My guess is that Arraez hits his maximum velocity mainly in hitters’ counts, and thus is seeing a lot of fastballs, while Acuna swings at these speeds mainly when in pitchers’ counts (and probably seeing more breaking balls).