Analysis: Nathan Eovaldi’s (Un)Lucky Season
If I asked you which pitchers have been the best in the American League this season, there would probably be many answers that come to mind. Gerrit Cole, despite his lingering foreign substance scandal, has still put together a solid year for the Yankees. Lance Lynn is proving to be the pitcher that Chicago expected him to be when they traded for him. Teammates Sean Manaea and Chris Bassitt have quietly been putting up great numbers for the Athletics. And this is not even mentioning the rebirth of Robbie Ray, the breakout season Dylan Cease is having, and the impact Jose Berrios might have on the AL Wild Card race.
However, if you look at the current AL pitcher WAR leaderboard on FanGraphs, you would find a rather surprising name at the top of the list:
Note: As of the day this was published, Eovaldi now has the AL pitching fWAR lead to himself, standing at 4.1 compared to Cole’s 3.8.
Much like the rest of the Red Sox rotation, Nathan Eovaldi hasn’t received much attention in 2021 - which makes sense given that Boston had the worst pitching staff in baseball last year in terms of combined fWAR. But even with the lack of fanfare, they managed to turn things around in Boston’s surprising first half, and they are currently fifth in that metric (with Eovaldi being their biggest contributor). Yet despite this success, Eovaldi’s surface-level statistics haven’t exactly convinced many people to turn their heads. Before his 7-inning, 10-strikeout gem against the Rays on Wednesday night, Eovaldi had a 9-7 record with a 4.07 ERA in 126 innings of work. To those who don’t believe in using more complicated metrics, this stat line makes Eovaldi look mediocre at best, and unremarkable at worst. However, when you delve into his underlying statistics, some fascinating patterns start to emerge.
You see, what makes Eovaldi so interesting to me is not his surprising fWAR total (which I will explain later on), but rather the fact that he has simultaneously been one of the luckiest and unluckiest pitchers in baseball this season.
To understand his strange luck, we must first understand FIP - or Fielding Independent Pitching - which is exactly what it sounds like. Essentially, FIP measures how well a pitcher controls the Three True Outcomes (i.e. walks, strikeouts, and home runs), and uses that information to determine what their ERA would be independent of the park he’s pitching in and the defense playing behind him - hence the name. If a pitcher’s FIP is lower than their ERA, it means that he is pitching better than his ERA suggests, and that a combination of bad luck and the defense behind him is costing him runs. However, if their FIP is higher than ERA, then the opposite is true.
Since FIP is meant to estimate ERA, most pitchers don’t have much of a gap between the two metrics. Typically, the difference for qualified pitchers is within half a run, and almost always less than a full run. With that being said, this has not been the case for Eovaldi. Among qualified pitchers in the AL, his 4.07 ERA is the ninth-highest in the league. His FIP during that time? 2.77, the lowest in the league. For those keeping track at home, that is a difference of 1.3 runs every nine innings that Eovaldi is being charged with due to factors outside of his control. The only qualified AL pitcher with a larger gap this season is Casey Mize (3.66 ERA, 5.06 FIP), and even then, his luck has flipped the other way. In other words, according to FIP, Nathan Eovaldi has been the unluckiest pitcher in the American League this season.
This brings us back to his aforementioned fWAR total, and why it’s as surprising as it is. For those of you who may prefer Baseball Reference’s brand of WAR, you might have noticed that Eovaldi’s 2.5 bWAR doesn’t even put him in the top ten on the American League leaderboard. So how is it that he is somehow leading the pack in one metric, but in the middle of the pack in the other? Well, the main difference here is that Baseball Reference’s pitcher WAR is based around Runs Allowed per 9 innings, or RA/9, while FanGraphs bases their measurement around FIP instead. Thus, while BRef punishes Eovaldi for his high ERA, FanGraphs heavily rewards him for his ability to avoid walks and home runs, which leads to a large disparity in the two metrics.
But even though I have been mostly discussing Eovaldi’s bad luck this season, it is actually his good luck that has allowed him to keep his FIP so low and his fWAR so high. As mentioned previously, FIP revolves around three main metrics - strikeouts, walks, and home runs. Typically, a pitcher can achieve a low FIP if they are able to strike batters out at a high rate, keep the ball in the strike zone, and get the ball to stay in the park. In Eovaldi’s case, he has been decent at striking out batters (his 8.86 K/9 is just 13th among qualified AL pitchers), but he has been phenomenal at attacking the zone and keeping the ball in play. In fact, his 1.71 BB/9 is the third-lowest among qualified AL pitchers, while his astounding 0.57 HR/9 is the lowest among that group by a decent margin. And it is the latter metric that I want to focus on here.
Throughout his career, Eovaldi has done a decent job of coercing ground balls, as his average ground ball rate for his career stands at 46.2%. However, especially in his last four seasons, almost all of his problems have come when the ball is hit in the air. Between 2016 and 2020, he had a ground ball rate that averaged just over 47%, but when his opponents hit fly balls, they turned into home runs nearly 20% of the time. Obviously, this was not good for the ol’ home run total, which resulted in a FIP of 4.98, 3.60, 5.90, and 3.87 in 2016, 2018, 2019, and 2020, respectively. But now, even though his ground ball rate has dropped down to its lowest level since he first got called up (42.0%), his performance has not been affected because his HR/FB rate has completely plummeted - all the way down to 6.5%.
With this in mind, it becomes clear to see what is going on here. During those years with the Yankees and Red Sox, he was already at a disadvantage as a right-handed pitcher in two of the easiest ballparks for lefties to hit home runs. But with a ball that was obviously juiced up during that time, all hitters had to do was flick their wrists and hit it around Pesky’s Pole. In other words, Eovaldi was probably one of the biggest victims of the Juiced Ball Era, and the results of this come through in his HR/FB rate over time:
2011 - 6.1%
2012 - 8.1%
2013 - 6.4%
2014 - 6.6%
2015 - 7.8%
2016 - 18.7%
2018 - 12.2%
2019 - 22.9%
2020 - 20.0%
2021 - 6.5%
So while he may be getting unlucky breaks defensively, there are at least two ways in which he has had luck in his favor this season. First, he was very lucky that MLB decided to “dejuice” the baseballs at the beginning of the year, a change that has allowed him to keep way more of his pitches inside of the park. But more importantly, even with the dejuiced ball, he has been getting very good batted ball luck on top of it.
For one thing, Eovaldi mostly pitches in Fenway Park - a notorious hitter’s park that especially caters to left-handed hitters. For another, Eovaldi throws a ton of strikes and doesn’t get a ton of swings-and-misses (37th percentile in MLB in Whiff Rate, 47th percentile in Strikeout Rate). With those two things in mind, we would expect that hitters would get lucky and hit at least a few homers over the short porch in right field. However, this has just not been the case so far this season. Much of this can be chalked up to Eovaldi doing a great job of avoiding hard contact (77th percentile in both Hard Hit % and Barrel %), but even when he does give up a hard hit, they somehow manage to stay in the yard, whether through luck or a bit of Manfred Manipulation.
To show how much Eovaldi’s batted ball luck has affected his performance, we can use a variation of FIP known as xFIP, or expected FIP. Much like how FIP predicts what a pitcher’s ERA would be without the defense behind them, xFIP predicts what a pitcher’s FIP would be if they had average batted ball luck. This is done by taking the HR portion of the formula and replacing it with the number of fly balls the pitcher has given up times the league average HR/FB rate. Again, since most pitchers have about average batted ball luck, there usually isn’t much of a difference between a pitcher’s FIP and xFIP. But again, Eovaldi isn’t average this year. In fact, when given a league-average home run rate, his FIP goes from 2.77 to 3.68 - a difference of nearly a full run. As was the case before, this was among the biggest gaps in the league, with Cole Irvin of Oakland (3.59 FIP, 4.72 xFIP) being the only qualified AL pitcher who benefited more from batted ball luck.
Thus, Eovaldi is simultaneously benefiting and suffering from an insane amount of luck in 2021. And as a result, he is statistically having one of the weirdest pitching seasons in baseball history. Whether or not he can keep this up the rest of the way is yet to be seen, but one thing is for sure: he’ll need luck on his side if he wants to help Boston sneak their way into a playoff appearance this season.