Saturday, July 29, 2023
Swing Speed - Run Values
We get the unsurprising results that the faster your swing speed, the better your production. The data represents the run value (per 100 pitches) on swings, based on the speed of the swing (relative to that batter's seasonal average). It includes hit into play, fouls, and whiffs.
Now, before you go out there and just swing as hard as you can, regardless of the incoming pitch, you have to understand the selection bias at play here. In a real MLB game, a batter always has the option to slowing down his swing. So, it's very possible that those times when he is +10 mph above his seasonal average, it's because he perfectly timed his swing to exactly the pitch and location he was expecting. When he is 10 mph below his seasonal average, almost assuredly he mistimed his swing, and/or tried to (unsuccessfully) check his swing, and so on.
We measure the swing speed at the impact point and so, all those factors play a role in the chart you see here. The ideal experiment would be to have a batter who maintains his swing throughout, regardless of the incoming pitch. Of course, if he did that, he would not be in the majors too long. So, as much as we'd like to think that swing speed is an input to the entire swing model, the reality is that the swing speed, as we're capturing, has a selection bias associated to it. And therefore, is not some independent input. As one data analyst noted forty years ago: let's be careful out there.