Jose Alvarado is throwing a WTF curveball

At least, until they change the name of it to a screwball

Look up the word “curveball” in the official glossary located on MLB’s homepage and you will see this as a definition:

A curveball is a breaking pitch that has more movement than just about any other pitch. It is thrown slower and with more overall break than a slider, and it is used to keep hitters off-balance. When executed correctly by a pitcher, a batter expecting a fastball will swing too early and over the top of the curveball.

Hmm, nothing there that gives an actual definition of what a curveball is, but read a bit further and this pops up [bolding mine]:

A curveball can be thrown with a number of different grips. Some pitchers possess curveballs with a sweeping, sideways trajectory, while other curveballs break straight downward. (These are known as 12-to-6 curveballs.)

The slider and the curveball are sometimes confused because they generally have the same purpose — to deceive the hitter with spin and movement away from a pitcher’s arm-side. (When a pitch seems to toe the line between the two, it is referred to in slang as a “slurve.”)

Now we’re cooking.

You might be wondering, why is this strange man telling me what a curveball is, officially? After all, you’ve seen one before. Like the Supreme Court, you know it when you see it.

Because by Statcast, Jose Alvarado is throwing one that sort of defies what the definition of a curveball actually is.

Let’s go back a bit. Last year, Alvarado threw three curveballs all season long. That’s a statistical nothing. In 2023, he didn’t throw one at all. In 2022, he threw eleven. So, basically, he had the ability to throw one, but perhaps it was lack of conviction, lack of desire, but for two years, he abandoned the pitch. This year, it seems he has decided that in order to have the kind of success he needs to secure more financial security from the team, he needs to add to his arsenal. It started this spring training, when Alvarado started throwing the pitch that confused pitch modelers online.

The games not being televised, we weren’t really able to see what the pitch was that was confounding people. A few weeks later, we got a much clearer look at what Alvarado was actually throwing. Here, you can see how the pitch is moving in a direction that really kind of defies the definition of what a curveball actually is.

You are like me (and that pitch modeler) and are confused. How can a ball that moves like that be considered a curveball at all?

And it’s not simply a one off thing that was going on during spring training. This year, even against Atlanta, Alvarado threw a curveball that had similar characteristics to the one that was thrown in spring.

So what gives? How can one call a pitch a curveball that doesn’t act like the one we see given definitionally by baseball? Let’s investigate.

First of all, let’s see the data on the pitch. According to Baseball Savant, Alvarado’s curveball (we’re only counting the ones in 2025 right now) are moving, on average, 46 inches vertically and 1.1 inches to the arm side.

The eagle eyed reader notices that there is more vertical movement than last year and a completely new direction horizontally from last year. So it makes sense that this becomes a head scratcher. The only thing to do is view the curveballs in action and see if we can make heads or tails from them.

Here is where we run into a problem.

Thanks to MLB creating the Film Room to help people search for things on a much more granular level, we can see all twelve of the curveballs Alvarado has thrown after Saturday’s game. Watch them all and you’ll find a common theme: a lot are in the dirt.

However, I wanted to focus on two of them. First, this curveball to Ozzie Albies, using the straight(ish) from center field camera, gives a really good view of that horizontal movement that we saw in spring training.

That ball is definitely moving to the glove side of Alvarado. It’s probably what causes the foul ball from Albies in the first place. The second pitch to focus on is the swinging strike thrown to Pedro Pages on Saturday.

From the naked eye, and judging from the swing by Pages, this is another curveball that is moving opposite of what we are believing a curveball to do. The data backs it up too.

So, what’s up?

If a curveball by definition is supposed to move to the pitcher’s arm side and this one, at least on average, does not, is it really a curveball? Shouldn’t the pitcher, team and MLB be reclassifying it as a screwball? After all, this is what a screwball is supposed to be doing: big, loopy and to the pitcher’s glove side.

We can state two things as a fact. One, Alvarado, at least as of now, throws a curveball. It’s what shows up on the broadcast, it’s what shows up in the official data points of MLB and it’s what he refers to it as. Two, this doesn’t move like a screwball is supposed to be moving. It might be subtle movement, not much at all, but it is still behaving different of what we believe a curveball is supposed to be doing.

Therefore, until (unless?) Alvarado renames this pitch as a screwball, I hereby dub it a “WTF curveball”. If we can have a sweeper, a kick change, and any other name used to describe pitches that we have watched for years, then we can have a new kind of curveball as well.

Jose, WTF?