Phillies: What’s Up With Aaron Nola?

Fastball Location

Aaron Nola operates with a four-pitch arsenal, utilizing a four-seamer, a sinker, a change-up, and a knuckle-curve. He owed much of his success in 2018 to keeping hitters off-balance at the plate through pitch mixing and movement, as opposed to than overpowering velocity.

That rings true this season, as his pitch-mix split and pitch velocities are virtually the same this year as they were during 2018. Seeing that pitch percentages and velocity aren’t the issue, perhaps we should take a look at the next most obvious suspect – pitch command.

Since August 25, Nola has had issues locating his fastballs, taking into account both his four-seamer and sinker. Typically, Nola makes his living by inducing whiffs and poor contact quality by locating fastballs on the outskirts of the strike zone, capitalizing on the natural run of his heater.

In his past four starts, however, these pitches have been catching far too much of the plate. Comparing Nola’s fastball heatmap before his start in Miami on August 25 to his heatmap after, we can see more fastballs have found the middle of the zone.

Hitters have taken advantage of these fastballs hovering over the middle of the plate, too. xwOBA is a metric developed by Statcast that conveys the expected weighted on-base average for a given batted ball, taking into account contact quality. In the 27 starts he made before August 25, his fastball was being hit for .342 xwOBA, according to Statcast.

Since, however, it’s been tattooed to the tune of a .412 xwOBA. As much as baseball has evolved in recent years, one surviving truth is that fastballs over the heart of the plate are easier to hit. If he’d forgotten that fact at all, Aaron Nola has surely been reminded of it in recent weeks.

If Nola can return to locating his heater on the outer parts of the plate, hitters would have a much more difficult time making solid contact with it. They also would struggle more in adjusting to off-speed offerings, which has been another culprit of the righty’s struggles.

Issues With the Curve

Aaron Nola owns one of the most effective curveballs in the game. In 2018, Nola’s deuce ranked third in pitch value among all curveballs, according to Fangraphs. As productive as the pitch is, it’s not nearly as fun to talk about as it is to watch:

In his past four starts, hitters have been getting to the pitch more than usual. In that span, they’ve managed a .361 xwOBA against it, compared to only .256 xwOBA before. How? Again, it comes down to location, as we can see a difference in where Nola has been spotting his hook.

Nola likes to bury his curveball down-and-in for lefties and down-and-away from righties. The above whiff from Daniel Murphy is an extreme case of the technique that nonetheless shows how deceitful the pitch can be when thrown this way. Recently, Nola has still been keeping his curveball low but has spread it out across the bottom of the zone.

With the launch angle revolution taking ahold of the game, batters are having an easier time getting to pitches low in the zone. Swings have more of an “upper-cut” aspect to them than they used to, enabling hitters to lift low pitches into the air. Low curveballs can still be effective if they’re sequenced properly or tunneled with a high-spin, up-in-the-zone fastball.

But, because Nola’s fastball is living more over the plate, his curveball doesn’t fool hitters like it’s supposed to. They’re swinging at it more often than they were before, and have been able to do more damage with it.

Nola’s curveball hasn’t differed in velocity, spin rate, or release point. It’s being thrown across the bottom of the zone, which when combined with a fastball living in the heart of the strike zone, has made it easier to hit.

When everything sits over the middle, hitters don’t have to worry about pitches that paint the corners of the zone. They’ll sit tight and wait for pitches they can get solid contact on. Nola’s been serving up pitches like that frequently over the course of this stretch, which is unlike his usual self.

Has Nola Just Been Unlucky?

Despite the shifts in the location of his fastballs and his knuckle-curve, there are two main statistics that may explain Nola’s recent struggles best. BABPIP measures the batting average of balls in play and usually stabilizes around .300. For a pitcher, a BABIP over that value is typically deemed as bad luck, whereas a value under .300 is regarded as luck.

LOB% measures the percentage of base runners stranded by a pitcher. In 2019, the league-average LOB% currently sits at 72.2%. Again, for a given pitcher, values above or below suggest luck may be a factor in the rest of their statistics.

If we compare Nola’s statistics from before and after his August 25 start in Miami, we can see that his BABIP and LOB% are drastically different. His BABIP jumped from .287 to .316, whereas his LOB% decreased from 79.6% to 63.8%.

It seems that luck played a role in Nola’s 2019 season prior to this recent stretch. He was benefiting from a BABIP lower than league average and a LOB% higher than league average. They both helped keep his ERA below his FIP, giving him decent overall numbers for the majority of the season.

Since August 25, however, his BABIP and LOB% have swung in opposite directions. This has thus induced the discrepancy between his ERA and FIP to flip, as well, with the former rising above the latter.

What does that mean on the whole? Well, BABIP and LOB% are two metrics that typically fluctuate over the course of a season, and ultimately stabilize at values that explain a pitcher’s true performance. A pitcher can outdo underlying metrics for stretches, but will likely also receive some bad luck at some point, too. Perhaps Nola is just in the middle of one of those unlucky stretches.

Can Aaron Nola Rediscover His Form?

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2019 hasn’t been kind to Phillies RHP Aaron Nola. After emerging as the staff ace in 2018, the organization and fanbase had high expectations for him entering this season. Although he’s displayed his Cy Young-level form at times, he hasn’t been able to hold onto it with much consistently.

Nola’s season has been a tale of stretches, with perhaps one of his worst coming at an unfortunate time. With the Phillies trying to stay afloat in the NL Wild Card Race, the righty has struggled to keep his team in games.

Over the past three weeks, Nola has had issues locating both his fastballs and his knuckle-curve. Not being able to throw these pitches where he’d like has allowed hitters to make harder, better contact. He’s leaving them over the center of the plate, and batters have been taking advantage.

Perhaps more explanatory of this string of starts is a swing in luck. It seems Nola was fortunate for much of the 2019 season, and this recent unlucky stretch is just luck averaging itself out.

Aaron Nola has regressed a bit in 2019, and this recent stretch is further evidence that this season has been below his standards.

However, that doesn’t mean that he can’t return to his usual form over the next three weeks. By living a bit more on the edges of the strike zone, and with a bit more luck, perhaps Nola can regain his ace-level production. The Phillies sure hope he does, because they need him.