Aaron Nola, In Three Parts
Philadelphia Phillies’ starting pitcher Aaron Nola has had interesting, but confusing, young career to date. The seventh overall pick in the 2014 draft, Nola was considered as polished a pitching prospect as you’re likely to see. While Brandon Finnegan was the first 2014 draftee to reach the Majors – notably pitching in both the College World Series and Major League World Series in the same season – Nola was close behind. After only 164.2 innings in the Minors, he debuted on July 21, 2015 and took no time to adjust. Known for his deceptive delivery, advanced command, and a strong fastball/curveball combination, he appeared to immediately live up to his mid-rotation projection.
However, a visualization of Nola’s 188.2 Major League innings would probably resemble something like a performance rollercoaster, and could be split into three different periods, each relatively equal in chronological time.
A lot of really great writing has been done about Nola’s career so far, and I’m going to reference a lot of it here. However, looking at Nola’s 2016 season line, I haven’t been able to square how well he did in almost all areas with how many runs were scored while he was on the mound. For instance, Nola’s 55.2 percent groundball rate was among the 10 best in baseball, minimum 100 innings pitched. His 19.1 percent K-BB rate was one of the 20 best rates. He didn’t even have an unusually high home run rate – it was exactly league average. It’s hard to be a pitcher with both a great FIP and groundball rate and still allow an above average number of runs.
So, let’s take a look at Nola, and not only take a look at what’s happened during each of these three periods, but also at what makes him successful in the first place. First, a quick acknowledgement to Mike Fast, whose old blog inspired some of the visualizations and tables below. His three part series analyzing then-player, now-manager Brian Bannister was particularly influential.
Let’s begin by taking a look at each period of Nola’s Major League career individually.
Period 1: 7/21/2015 – 9/26/2015
Aaron Nola debuted mid-July 2015, and over the remainder of the season, looked exactly as advertised. The above table shows that during this time, he threw an efficient number of pitches per inning, had a healthy strike rate, and had peripherals commensurate with a mid-rotation starting pitcher. He deserves a little bit of extra credit for doing this at age 22 without requiring a single inning to adjust to the Majors.
Not only did he bring his deceptive delivery and command to the Majors, he also brought his advanced understanding of sequencing. The below table using PitchFX data shows both the total usage of each pitch and the rate at which each pitch was sequentially followed by every other pitch.
|Previous Pitch||Total %||FF||SI||CU||CH|
For example, the most immediately noticeable trend was that curveballs almost never followed changeups during this time (only in 1 percent of all cases). Besides that, it is clear that Nola is not afraid to mix it up. He’s not afraid to double up on pitches, and there’s a least a decent chance that he’d use any combination of two pitches. Additionally, his stellar curveball wasn’t used quite as much as it could’ve been, and he pretty evenly divided his fastball usage between fourseamers and sinkers.
Period 2: 4/6/2016 – 6/5/2016
Aaron Nola showed up in 2016 looking like an ace. Through his first 12 starts of the season, Nola was one of the best pitchers in baseball, showing an increased strike rate and ability to miss bats. His strikeout and groundball rates jumped, his walk rate decreased, and the contact made against him was weak.
Over at FanGraphs, Alex Chamberlain wrote about how Nola’s ability to generate called strikes with a well-commanded, explosive sinker contributed to his success. Jeff Sullivan wrote about how his curveball might be the best in baseball. August Fagerstrom added that his command and deception made him one of baseball’s best young starters. Nola was doing a lot of things right.
Let’s check back in with the usage and sequencing table, updated to reflect this time period.
|Previous Pitch||Total %||FF||SI||CU||CH|
What stands out here is the increased reliance on the sinker over the fourseam fastball. Its combination of movement and command helped generate a lot of called strikes and groundballs. He also pulled back a bit with changeups overall, but was really willing to double down on the pitch, following one changeup with another changeup almost a quarter of the time. That might have just been a (successful) attempt to freeze batters – if they weren’t expecting to see his least-used pitch once, they probably aren’t expecting to see it back-to-back.
Period 3: 6/11/2016 – 7/28/2016
This is when everything fell apart. Nola’s strike rate fell significantly, and was worked hard (he jumped to nearly 20 pitches per inning). His K-BB rate fell over 40 percent, and his hard-hit rate jumped dramatically. Looking at this period’s usage and sequencing table, there’s nothing incredibly different that stands out. Aside from using a few more fourseam fastballs, it doesn’t look like something problematic changed in his approach.
|Previous Pitch||Total %||FF||SI||CU||CH|
During this time, Eno Sarris wrote that fewer batters were being fooled by a slightly flatter, more poorly commanded sinker. Former Crashburn Alley managing editor Corinne Landrey noted that his stuff hadn’t changed, but his command was noticeably off. Despite hoping that he’d make a tweak or take a mental break that would fix the problem, Nola continued to struggle until being placed on the disabled list after his July 28th start.
Frighteningly, this was due to an elbow strain, and after being placed on the 60-day disabled list, his season was over. It is not clear exactly how long Nola had been affected by this injury, but it came at the end of what the team called an eight start “dead arm” period, a general fatigue related to the shoulder that deprives pitchers of their ability to place pitches with their typical precision. Fortunately, this is typically seen as a temporary issue that can be worked through by continuing to pitch – however, it isn’t clear if an attempt to work through this problem contributed to the season ending injury.
We have a pretty decent broad view of the arc of Nola’s time in the majors, but let’s take a look at his repertoire – what are the features of each pitch? Did the velocity or movement of each really not decline during the “dead arm” period? When is each pitch used, and has that usage changed at any point?
We have the general impression that Nola’s “stuff” (pitch movement and velocity) didn’t decline during the third period we’re discussing. The below GIF is a polar scatter plot, split into one of three time periods. For each pitch, its angle direction indicates the direction of its movement (a pitch at zero degrees breaks straight up), while its distance from the center of the circle indicates its velocity.
Obviously, as the third period saw significantly fewer innings pitched, it also has a smaller sample of pitches in the above chart. Just by casually observing this plot, it seems like his pitches (particularly his fastballs) lost a little bit of drop in the third period, and there were a few more pitches straddling the lower bounds of their earlier velocity ranges (there are a few more fastballs hovering around the 85 mph band). A few of the fastballs and changeups almost blend together in terms of velocity, and that lack of separation can be a detriment to both pitches. These are relatively small changes, and alone wouldn’t mark a drastic decline.
We saw on a macro-level how Nola’s usage changed over time, but let’s look at a rolling usage by start to see if there are any apparent trends.
Interestingly, fourseam usage continued to decrease throughout the stellar middle period, and changeup usage only picked up towards the end of that same period. Splitting by count, and batter handedness, the same data shows an addition couple of interesting points.
There’s a couple obvious points – in 3-0 and 3-1 counts, a batter’s almost always going to get a fastball. Nola relies heavily on the curveball with two strikes. He favors using the changeup against opposite-handed batters. What can also be seen is the dramatic drop in fourseam fastball usage between 2015 and 2016. However, against same-handed batters, that usage ticked back up in the third period.
One thing that I wanted to try was to see Nola’s decreasing strike rate could be seen in his mechanics. The hypothesis here is that repeating a consistent release point is seen as a hallmark of good command, so measuring the amount of change that occurs throughout a start (in this case, the statistical variance of the release angle) could give an indication of that. This was plotted using the release point data from MLB Gameday’s publicly available PitchFX dataset.
The increase in the middle falls in line with the altered position on the pitching rubber Nola debuted at the beginning of the 2016 season. Because we don’t know have a relative measure of the league average release point variance in a single start, the significance of a change from 1.2 degrees of variance to 2.6 degrees isn’t certain. As a hypothesis though, it does coincide with Nola’s “dead arm” and lowered strike rate.
So far, we know that Nola maintained his advanced approach to opposing batters and saw only a small decline in stuff during his “dead arm” period, but may have had more significant problems with command. Now we’ll look at his individual offerings and see how each’s command and results changed over time.
Nola’s fourseam fastball dropped significantly in use between 2015 and 2016. The most incredible thing about the above table is the called strike percentage – during the first 12 starts of the 2016 season, over 30 percent of his fourseam fastballs were called strikes. This isn’t unique to this pitch. Per Baseball Reference, in 2016 36 percent of Nola’s strikes were strikes looking. That’s the highest rate of anyone with at least 15 innings pitched (a ridiculously low threshold). The second highest for a starting pitcher (minimum 100 innings) was fellow fastball-curveball madman Rich Hill.
During the third period, his called strike rate did decline significantly, as did the total strike rate. Let’s take a look at a plot to see more.
The number of called strikes in the zone during the first two periods is pretty substantial. However, in its limited use during the third period, Nola missed lower and away more often to batters on both sides of the plate. Again, at that point it was already a smaller factor in his repertoire, but it didn’t help his struggles.
Nola added almost a full inch of horizontal movement to his twoseamer between 2015 and 2016, and threw it for five percent more strikes. With Nola making it move more with better command, a batter is more likely to mistakenly expect a ball. They don’t swing, and instead the pitch moves 11 inches back over the plate. A pitcher that can do that regularly is dangerous.
Again, note the large concentration of called strikes on sinkers to both sides of the plate. A lot of ground balls can also be seen throughout the strike zone to both left and right-handed batters. Looking at the plot between 2015 and 2016(a), it looks like there’s a shift in location against right-handed hitters. Whereas in 2015, Nola threw the pitch arm side to everyone, he was able to throw to both sides of the plate by opening day 2016. Negatively, he also lost over an inch of horizontal movement during period three, potentially effecting the pitch’s ability to fool batters.
Like everything Nola throws, this is another pitch with a lot of horizontal movement. The whiff rate has been impressive, and, yet again, so was the called strike rate. Since it’s used most frequently in two-strike counts, it is aptly Nola’s “out” pitch. There was a little bit of decline in command, but it looks like its quality was largely maintained during the rough patch.
He absolutely knows how to locate this pitch – Aaron Nola has basically never accidentally thrown a curveball on the up-and-armside portion of the strike zone. Generally, there’s an apparent pattern for this pitch. Higher in the zone, the curveball receives a called strike. Lower in the zone, this pitch generates groundballs and whiffs. Below the zone exists a black hole for contact – look at all those red dots for swinging strikes.
The changeup is Nola’s third pitch, and I think that the high whiff rate to begin 2016 was due in part to both small sample and the timing of its use as opposed the inherent quality of the pitch.
This is another pitch that Nola is able to locate really well, and it is an effective offering against opposite handed batters. It really wasn’t used enough during period three to say much about it, but if he can continue to place it down-and-away to lefties, it should be a productive offering.
On November 2, Nola’s agent announced that he had completed a throwing program and has been declared healthy by Dr. James Andrews. The fact that he’s suffered low-grade UCL damage is still something to remember, but everyone should be cautiously optimistic moving forward. The results over his last eight starts were objectively awful, but it doesn’t look like anything related to Nola’s “dead arm” is a long term concern.
There’s evidence that during this time, his velocity dropped ever-so-slightly, and his offerings saw a little less explosive horizontal movement. He was definitely less able to throw strikes, and a combination of those factors allowed opposing batters to make better decisions about when to swing at his pitches. Ideally, moving past the dead arm returns his command and stuff to his prior levels, and with those returns his deception.
Not to tie myself to an easily disprovable opinion, but I think that moving forward, he might be closer to the staff Ace we saw to begin 2016 than even the mid-rotation starter he appeared to be in 2015. Given what we’ve seen from him, there’s a really strong argument to be made that he is still the best starting pitcher on the Phillies, struggles be damned.