Aaron Nola 2021 Year-in-Review

Phillies right-handed starting pitcher Aaron Nola was one of the most dominant pitchers in the league in the short 2020 campaign. That season along with the upside we had seen from him previously, and his young age made him an SP1 on fantasy rosters coming out of the draft. Nola went in the top two rounds in most drafts but fell quite flat in 2021, stumbling to a 4.63 ERA and a 1.13 WHIP over his 180.2 innings pitched.

Those final numbers will certainly send his draft stock plummeting in 2021, making him a name that will generate lots of discussion in the lead-up to drafts next spring. Nola has proved over his career to be a tough nut to crack, giving up very little in terms of consistency year to year. In this article, we will do our best to get a hold of what happened in 2021 and make some educated projections as to how 2021 may go for him.

First, let's take a look at what the last five seasons have brought for Nola.

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Getting to Nola

This season was his first truly bad season as far as ERA goes. We know that ERA is not a reliable predictive measure, and we should not pay a ton of attention to it. However, it still does remain a strong statistic for looking back at what actually did happen on the field. He just didn't help the Phillies win much last year. Let's spend a little bit of time on this table before getting deeper into things.

K-BB Rate

Subtracting Nola's 5.2% walk rate from his 29.8% strikeout rate in 2021 gives us a difference of 24.6%. That is an elite number that ranks 26th amongst all pitchers that threw at least 150 innings in a single season since 2015. There is a distinct linear relationship between K-BB ratio and ERA. As the K-BB ratio gets bigger, we expect the ERA to shrink. I have plotted this relationship using all pitchers since 2015 who have thrown at least 100 innings in a season to show the trend:

So a clear downward slate there. It is very hard to have a K-BB% above 20% and post an ERA above 4.00. Since 2015, 113 pitchers have thrown 100 innings with a K-BB% above 20%, only 15 of them have come in with an ERA above 4.00. Nola's 4.63 mark in 2021 is one of those. You can see how high his dot is floating above the trend line.

We probably cannot just stop right here and chalk up the bad ERA to bad luck, but bad luck is definitely a suspicion we should have.

Ground Ball Rate

The biggest red flag on the table we initially showed here was the career-low ground-ball rate that Nola put up this past season. His career ground-ball rate now sits at 48.7%, so far above the 40.5% we see for 2021. So what happened there? The first thing we would suspect is that he threw fewer sinkers. The reason for this is because the sinker is by far the pitch most conducive to the ground-ball. Checking on his pitch mix over the last five years, we see that our suspicion was correct:

Nola dropped his sinker usage down from 21% to 14%. You may notice that he threw his sinker at even lower rates in 2018 and 2019, but still posted high ground-ball rates. What counters that is the extra curveballs he threw in those years. The curve also gets ground-balls at high rates due to the downward motion of the pitch.

So if we add curveballs plus sinkers for each year to find what percent of the time he was throwing one of his ground-ball pitches, we see these numbers in order from 2017 to 2021: 52%, 44%, 46%, 48%, and 41%. If we would have known he would have made this change to his arsenal before the year started, we could have predicted a significant decline in ground-balls, but I doubt we would've taken him the whole way down to 41%.

Home Run Luck

You might think that given the strong strikeout and walk numbers but bloated ERA, Nola suffered from a serious home run issue. This is usually a prime suspect when we see an ERA much higher than expected, but in Nola's case it doesn't seem to have been an issue. Nola's HR/FB rate was 20.1%, just one point above the league average of 19.1%. His average exit velocity on fly balls was 91.3, coming in under the league average of 92.2, and he posted a pretty average fly ball rate (26.9%) and barrel rate (7.1%) as well (those league averages are 25.6% and 7.9% respectively).

While his performance didn't stand out as compared to the league average, it did stand out when compared to the rest of his career:

Nola's 2020 season was certainly an outlier. A 39% HR/FB rate is a true outlier result, and the 13.7% FB% is also very, very hard to do over the long haul. Things really went Nola's way in the short 2020 season, and those numbers bounced back to league average numbers in 2021. I think Nola is a guy that should be beating the league average in barrel rates and HR/FB numbers given the quality of his stuff and his ground-ball ability, but that didn't happen in 2021 and it hurt his final numbers quite a bit.

Count Analysis

You would think based on the low walk rate he posted that Nola got ahead in the count a bunch. I wondered if maybe this wasn't true, and he ended up getting himself behind in the count often and decided to just continue to throw strikes, making him a more predictable pitcher. This didn't turn out to be the case.

In 2021, Nola threw 34% of his pitches while ahead in the count (I defined this as 0-1, 0-2, and 1-2 counts), which was the highest mark of his last five seasons. He threw just 4.9% of his pitches while behind in the count (2-0, 3-0, 3-1). Nola had his second-best first strike rate of the last five years (second to only 2018) as well, so putting himself in good positions on the mound really wasn't the issue in 2021.

Pitch Performance

So far we haven't found much to explain Nola's hugely disappointing performance in 2021. I made one last-ditch effort to try to figure something out, checking on how each pitch performed individually this year as compared to his last four seasons. Here are the called strike plus whiff rates (CSW%) Nola has posted with each pitch over the last fives seasons:

You can see that every pitch was worse in 2021 as compared to 2020, which isn't surprising since that 2020 season was such an outlier, but even looking at 2019 we see major regression. The 20.6% CSW% on the four-seam fastball is just bad. The league average CSW% on four-seamers is 26%. It's true that Nola has never dominated with the four-seamer (as you can see he's yet to post a 26% CSW on the pitch), but the 20.6% is really far down there. 9.2% of that CSW% is made up by whiffs, and honestly, that's not a horrible SwStr% for a four-seamer. He just really did not locate the pitch very well or fool hitters with it to the point where he was generating a ton of called strikes with it.

Let's sum up the pitch mix analysis here with some bullet points.

• In 2020, Nola threw four pitches at 20% or higher, making him one of the least predictable pitchers in the league.
• In 2021, Nola upped his four-seamer usage at the expense of his changeup and sinker. This, no doubt, contributed to his lower ground-ball rate, but didn't result in an outrageous amount of homers allowed.
• The curveball is Nola's best pitch, but it has to come in tandem with a strong fastball or good duo of fastballs (four-seams and sinkers that look the same out of the hand but move differently), or else it loses some effectiveness.
• His velocity on all pitches stayed the same as we've come to expect from him.

It was probably foolish to expect Nola to keep that 2020 pitch distribution where he threw four pitches at very similar rates, that's just not something that a pitcher wants to do when they're expected to throw 170+ innings. It was surprising, however, to see him throw so many four-seamers and so few sinkers. That said, we've seen Nola throw the four-seamer above 35% of the time before with much better results. It's not a horrible pitch, but it really didn't work well for him in 2021.

Conclusion

All of this is to say that I'm not really sure what happened with Nola in 2021, but it's pretty clear that he ran pretty cold in the luck department. His xFIP was a strong 3.37 and his xERA shows at 3.39, both of those marks crush the 4.63 ERA he posted. Those expected numbers are largely derived from strikeouts, walks, and home runs allowed, and we saw immediately in this post how good Nola's K-BB ratio was in 2021. That makes it no surprise that his ERA predictors would be much better than what we saw in reality.

It's too early to look at ADP data, but I am likely going to be very, very interested in drafting Nola in 2022. He will be just 28 years old on Opening Day, and he pops off the page when looking at K-BB ratio. He was 5th in the league in that category in 2021 behind just Corbin Burnes, Max Scherzer, Gerrit Cole, and Robbie Ray. The field is sharp these days, and very few fantasy baseball managers will go into the draft not being aware of that fact, so we will have to wait to see how far the ADP falls before calling Nola a priority in drafts, but I do expect to be very bullish on Nola next season.

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