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So you want to assess batter output... are bat speed and EV interchangeable? Was talking with @Tstokey about the benefits of looking at each, and some quick back-of-the-envelope diagnostics that I've found helpful to lean on in answering that question. 1/
As we've covered extensively, our go-to output KPI @DrivelineBB is Top 1/8th exit velocity. It eliminates 'noise' by scrubbing mishits to drill down on a hitter's "true" capacity to impact the ball -- making it far more reliable year-to-year than Avg EV 2/ https://www.drivelinebaseball.com/2019/12/driveline-hitting-kpis/
Naturally, honing in on flush contact for our EV metric pushes it in line with avg bat speed -- we've eliminated the *vast majority* of batted balls where some bat speed is 'wasted' with non-solid contact (R2 = .87 in-gym). But what about when that relationship breaks down? 3/
Internalizing how bat speed SHOULD translate into EV enables us to sniff out cases where it doesn't -- and start understanding why. The most common cause to turn to is poor quality of contact: even on a hitter's best balls, they still aren't squaring it up consistently 4/
It can help to take a step back and think about a) what tools we're using and b) how they measure. Bat sensors record bat speed at a single moment just before contact. The longer you have to accelerate the bat, the higher your measured bat speed, making POC worth consideration 5/
A hitter may have an average POC so far out in front that it fails to produce solid contact, despite generating great bat speeds! It may take significantly deeper contact for them to flush a ball, forcing bat speed and top 8th to diverge from our expected relationship. 6/
This can also work the other way, with players who hit the ball exceptionally deep struggling with bat speed yet exceeding expected EV. Like other metrics, bat speed and EV work perfectly fine alone for most guys, but closer to the edge there's value in using them in tandem. 7/
