Dan Altavilla’s new (ish) slider

We’re three games into the 2017 season which means we’ve got real data to analyze. Rather than overreact to the offensive impotence we’ve witnessed during this opening series, I want to hone in on one pitch in particular: Dan Altavilla’s slider. Like Edwin Diaz, Altavilla made the transition from the rotation to the bullpen last year and made his major league debut straight out of Double-A.

Yesterday, our esteemed broadcaster Aaron Goldsmith tweeted the following after Altavilla’s debut on Tuesday:

The velocity difference Goldsmith points out is certainly interesting (though not that interesting as you’ll soon find out) but a new grip gives us new pitch characteristics to analyze.

Before we get too deep into the analysis, I want to first address some important changes in how pitch data is presented to the public. Earlier this week on FanGraphs, Dave Cameron revealed that MLB has changed the way pitches are tracked beginning this season. Since 2007, PITCHf/x has been the primary provider for pitch data, but with Trackman now installed across the league, MLB has converted to the Statcast system. Since PITCHf/x is a camera-based system, many of the data points we’re familiar with were extrapolated from the raw data. Trackman is a radar-based system meaning the data it gathers is far more accurate.

This change in data providers means that there are some changes in how data is reported. PITCHf/x reported pitch velocity numbers at a defined point along a pitch’s path (around 50ft from home plate). Statcast is now reporting pitch velocity from the pitcher’s release point (the highest point of velocity). (It bears mentioning that Brooks Baseball manually adjusted the PITCHf/x velocity data to account for a release point closer to 55ft from home plate, which is much closer to the Statcast data in aggregate.) You can read more about this change here and here. It’s still unclear how the new data affects pitch movement data. For now, I’ll be assuming there is no discernable difference (with the obvious caveat that we’re treading new ground for now).

With all that out of the way, let’s get back to Altavilla’s slider. I pulled his pitch data from Baseball Savant and adjusted his 2016 velocity to better correlate with this year’s data.

We’re obviously working with some very small samples here but some differences are immediately apparent. After two appearances, Altavilla is throwing his slider a little less than a mile per hour slower than last season. In his appearance on Tuesday, his average slider velocity was 89.4 mph while it was just 88.4 mph last night. I don’t think there are any conclusions about his slider velocity we can draw yet after just two appearances.

We can also see that Altavilla’s new grip has imparted some different movement on his slider. He’s lost some horizontal and vertical movement off the pitch. But he’s also added 200 RPM to the pitch’s average spin rate. In general, adding spin rate to a slider is going to make it more difficult for a batter to pick up.

For comparison’s sake, here are a pair of gifs showing a slider from last year and from last night. The camera angles are a little different but I think you can see the difference.

9/23/2016

4/5/2017

The difference is hard to spot. His new slider looks a little more like a cutter than a true slider. In terms of results, he’s generated a whiff more than half the time an opposing batter swings at the pitch this season. It’s still a nasty pitch.