Yovani Gallardo Has Two Sliders

During his first start for the Orioles on April 11, Gallardo threw 96 pitches - 67 of which PITCHf/x determined to be sliders. A look at the movement of his 96 pitches (with gravity - this is what the batter saw) shows two very distinct clusters of sliders. One looks the way you might expect a slider to look: dropping lower in the zone, traveling from left to right across the plate. The other cluster stayed up, dropping about 10 inches with the help of Mother Nature, and never actually slid. Instead, the second bunch of sliders stayed straight. They look the way you would expect a fastball to look.

PITCHf/x classifications are determined today by algorithm, although it has been done by hand in the past. It's certainly possible that these are simple misclassifications as a result of that estimation model. Gallardo's fastball was only thrown about 4 miles per hour faster on average than his slider - a major difference, but one that can easily be spanned by arm fatigue. Gallardo's fastest slider on April 11 was thrown at 87.5 miles per hour. It's entirely conceivable that an algorithm could label an 87.5 mile per hour slider that doesn't slide as an 88 mile per hour fastball.

At the same time, Gallardo has a short bit of a history with these two types of sliders. The vast majority of Gallardo's straight sliders is from 2015 onward, indicating that he could have added a slider with a different spin and a different movement path to his arsenal. According to PITCHf/x, Gallardo is also increasing the number of sliders he throws every year. If there were a sudden spike in slider usage, I might be more apt to consider it a fluke pointing to an issue in the algorithm's ability to classify Gallardo's pitches.

This leaves three possibilities (or some combination thereof, I suppose) to explain why PITCHf/x thinks Gallardo is throwing so many sliders, and in two distinct types. The first is that PITCHf/x is simply misclassifying Gallardo's fastballs as sliders for some reason and with some regularity. The second is that Gallardo actually did throw an obscene amount of sliders on April 11 and that they have always been more common for him than fastballs, he just isn't getting the break on them the way we would want to see. The final possibility is that Gallardo actually has two sliders that he throws in two different ways, on purpose, for different effect.

John Walsh at the Hardball Times put together a helpful pitch identification primer in 2009, in which he describes sliders as generally falling between fastballs and curveballs in terms of both speed and movement. He also identifies sliders that don't have any horizontal spin or break at all, pitches with essentially no movement. Here's how he describes the specific subset of sliders that we are possibly seeing from Gallardo:

[I]f the axis of spin is aligned with the direction of the pitch (like a football toss, or a … gyroball), there will be no break. I believe this is what we are seeing when we see a pitch with no movement. I wouldn’t call these gyroballs, by the way. Or maybe I should—in any case, a number of different pitchers throw sliders that fit the description, and I don’t believe it’s anything new.

While it's pretty cool to throw the same pitch two ways for two different effects (which, uh, might make them two pitches?) - if that is the case - it hasn't necessarily helped Gallardo. His batting average allowed on decisive sliders - ones that ended the plate appearance - from 2012 through September 2015 is 0.239, while his slugging percentage on decisive sliders is 0.370. When it's broken into the two categories of sliders, it's clear that one is more helpful than the other.

Pitch Type	Times Thrown	Batting Average	Slugging Percentage
Traditional Slider	3,987	0.233	0.359
Straight Slider	61	0.328	0.361

Pitches in red are what I'm calling Straight Sliders.

Notice that Gallardo hasn't thrown what I called a straight slider very often over his career. However, 49 of those came in 2015 alone, and he looks to have thrown about 20 in his first 2016 start as well. While the straight slider hasn't burned Gallardo for extra bases yet, it's worth keeping an eye on. If he means to get movement across the plate, it's a major issue that Gallardo is suddenly less and less capable of doing so. If he is using a straight slider as a pseudo-fastball for some reason, batters seem able to hit it pretty well. Gallardo's next few starts for the O's may shed more light on whether he's actually throwing this many sliders and whether he's throwing straight ones on purpose. If the latter is true, we're probably in the process of watching Gallardo reinvent his pitch arsenal, and arguably to one that gives up more hits.