Aaron Nola Has Baseball’s Best Curveball

How do you identify the very best pitches? It’s actually not easy, since every pitch in someone’s repertoire has an effect on every other pitch. So let’s say this: I don’t know if Aaron Nola’s “true-talent” curveball is the best in the game. What I know is, to this point, it’s been the most effective curveball in the game. By lots! Here’s the top of the run-value leaderboard for curves in 2016:

1. Aaron Nola, +9.5 runs
2. Jerad Eickhoff, +3.6
3. Carlos Carrasco, +3.2
4. Justin Grimm, +3.1
5. Aaron Sanchez, +3.0

Nola’s value is nearly the sum of the next three values combined. How great is +9.5 runs? Only one pitch so far has a higher value, and that’s Jose Quintana’s fastball, at +10.0. Quintana has thrown almost 400 fastballs. Nola has thrown fewer than 200 curves.

We’ve written plenty about the Phillies so far. Countless people have, because the Phillies have surprised, and it’s no secret the key to that has been unbelievable pitching. This has become the core of the Phillies’ whole rebuild, and they love what they’re getting from Eickhoff. They love what they’re getting from Vincent Velasquez. But you can’t forget about Nola. Nola was always thought of as the safe, polished one, but now he’s flashing upside, such that he might be the best of them all. He might be turning into one of the best, period, and the curveball is fueling his ascent.

Nola has long been recognized for his breaker. It was his calling card as a prospect, the pitch that made him a prospect. It performed well in Nola’s debut season, so it clearly held up against big-league opponents. Nola, this year, has lowered his ERA- by 22 points. He’s lowered his FIP- by 42 points, and he’s now striking a bunch of guys out. We’ll talk more about the curve in a bit, but we should acknowledge that Nola has also improved his fastballs. Every pitcher will tell you the secondary stuff is nothing without the primary stuff. So let’s quickly look at how Nola’s improved his primary stuff.

Nola has two variations of a tailing fastball, and he’s gotten more aggressive — where last year he threw 49% of fastballs in the zone, this year he’s shot up to 57%. This is a guy who wasn’t blessed with tremendous natural velocity, but he does get into the 90s, and Nola has demonstrated plus command. He’s able to mostly stay to the sides, and it stands to reason Nola would be benefiting from improved angles. Here’s Nola delivering a pitch last summer:

And here’s Nola delivering a pitch recently:

If you look closely, you see that Nola has shifted to the first-base side of the rubber. It’s a difference of almost a foot, and when Nola gets to his release, he drops down, almost sidearm. His slot is extreme, but now he’s a little more direct to home plate. This is my own speculation, but by facing the zone more head-on, Nola could have a better understanding of how to hit each edge cleanly. There’s a deception edge with the old release, at least as far as facing righties is concerned, but now Nola can keep his fastballs a little sharper with a lefty in the box. I’ll note that, against lefties so far, Nola has just about doubled his strikeout rate.

So Nola is attacking more with his fastballs. He’s shown a better ability to locate, and Nola, overall, has a league-leading rate of strikes. By commanding the edges with fastballs, Nola is really allowing his breaking ball to flourish. This is the really fun stuff. Here’s the curveball in slow motion:

That’s interesting, just visually, although the pitch didn’t generate a swing. Here’s a first-pitch curveball for a strike:

Dangerous pitch (ed. note: in Nola’s favor, I mean). Here’s a second-pitch curveball for a different kind of strike:

That’s not very polite. See, Nola has a refined understanding of how to throw his curve. He can throw it in the zone when he wants, and he can throw it below the zone when he wants. Pulling from Baseball Savant, here are curves with zero or one strike:

And, the two-strike curves:

You see that he uses the pitch in two ways. This makes the pitch more dangerous than usual, because as a hitter, you might identify the spin, but you don’t quite know where the ball will end up. Hitters can’t ever eliminate the curve, but it’s also tough to sit on, because Nola loves to use it to get hitters to expand. The feel for the fastballs is there. The feel for the curveball is there. Nola hasn’t even really needed his changeup to look like an ace.

Let’s stay with the deep dive! One thing that makes Nola’s curveball outstanding is his feel for the pitch. Another factor is the pitch’s movement. I pulled all curveballs and sliders thrown this year from the Baseball Prospectus PITCHf/x leaderboards. The only breaking ball with more horizontal movement in the whole spreadsheet is Sam Dyson‘s slider, but Nola’s curve gets more than four inches more drop. Corey Kluber’s breaking ball also has similar horizontal movement, but Nola’s curve gets about six inches more drop. It’s a very unusual pitch that he throws, in large part being a function of his arm angle. Hitters aren’t accustomed to seeing that, so to go with the fastballs and the breaking ball, you get to fold in deception.

I’ll note as well that the curveball’s success hasn’t been lost on Nola. He knows full well what he can do, and he’s throwing his pitches with a more advanced mix. Instead of throwing curveballs a quarter of the time, like last year, Nola now is throwing them a third of the time. He’s throwing more first-pitch curves. He’s throwing a lot more curves when behind in the count. The pitch is still there as a two-strike weapon, but Nola also knows how to keep hitters off balance. Here’s maybe my favorite measure of the curveball’s effectiveness. When the curveball has been in the zone, hitters have swung 46% of the time. When the curveball has been out of the zone, hitters have swung 46% of the time.

Right there, that partially indicates one thing that makes Nola strange. I mentioned the deception. Nola gets a good number of swings at would-be balls, but he also manages to avoid swings at strikes. What would be better than a pitch in the zone, that’s taken? Here’s a table of qualified pitchers, sorted by the smallest differences between zone-swing rate and out-of-zone swing rate:

Nola has a difference of 15 percentage points. Second place is all the way up at 22. The average is 33. So that’s a massive lead, and you can see that Nola also peppers the zone. So it’s not like hitters are waiting because they don’t trust his location. Nola isn’t Ubaldo Jimenez. Nola is up there just confusing all his opponents. He’s done it in an extraordinary way, which is maybe befitting of an unconventional prospect. Nola isn’t particularly tall, and he throws with a very low slot, and in the minds of scouts, that introduces uncomfortable uncertainty. But based on the results, you could say hitters against Nola are also characterized by uncomfortable uncertainty. They don’t know when they’re getting strikes or balls, and as such, Nola is thriving.

It’s important to note Nola hasn’t been sending these signals all along. Even in the minors, he struck out just 21% of opponents. He wasn’t supposed to become a strikeout pitcher — he was supposed to become a stable pitcher, a low-walk pitcher. What he looks like today is indeed a stable pitcher, and a low-walk pitcher, but now he’s mixing in third strikes on top of all that. With tighter command of his pitches and a different angle to the plate, Nola is starting to look like a legitimate ace. We’ll see if time allows the league to figure him out, once everyone grows more accustomed to what he has, but if anything the trend is going in the opposite direction. The evaluators were right: As a prospect, Aaron Nola was safe. It’s the upside they underestimated.