What’s Wrong With Seth Lugo?
There was a time in the not-so-distant past when Mets fans loved and trusted Seth Lugo. Though his workload restrictions frustrated them, fans felt good about their chances when he was in the game—and for good reason. When he moved to the bullpen in 2018, he posted a 2.30 ERA and 3.45 K/BB in 78.1 relief innings. In 2019, Lugo had another good year as a reliever with a 2.70 ERA and 6.50 K/BB in 80 innings. Lugo looked like a dominant reliever, too—he had one of the highest spin curveballs in the league, which produced swings like this:
Fast forward three years, and many Mets fans don’t want to see Lugo in high-leverage spots anymore. In 108.2 innings since the start of 2020, Lugo has an underwhelming 4.06 ERA. For some, his blown save against the Dodgers last week was the final straw.
So, what happened? The curveball is still spinning, and he hasn’t really lost any velocity. Well, it’s not as bad as it looks. The data is skewed by 6.15 ERA as a starter in 2020. If we limit our sample to his relief innings, he has a 3.39 ERA since 2020. That may not be elite, but it’s good for an 86 ERA- and a lot better than 4.06.
If we had to draw a line where Lugo transitions from a dominant reliever to merely a good one, it would probably be the start of the 2021 season. Before his 3.50 and 3.51 ERA in the last two years, Lugo had never posted an ERA above three as a reliever. So, let’s divide Lugo’s relief career into two parts—dominant (2016-2020) and good (2021-2022)—and compare the two.
| IP | ERA | ERA- | FIP | XFIP | SIERA | wOBA | K% | BB% | K-BB% | HR/9 | |
| Dominant | 188.2 | 2.53 | 64 | 2.88 | 3.44 | 3.12 | .242 | 28.3% | 6.3% | 21.9% | 0.72 |
| Good | 72 | 3.50 | 90 | 3.70 | 3.62 | 3.48 | .299 | 25.9% | 8.3% | 17.6% | 1.13 |
There is a 0.97 R/9 difference in the two ERAs, but the ERA equivalents—FIP, xFIP, and SIERA—all suggest a smaller decrease in skill. It’s certainly possible that xFIP and SIERA are correct and that most of the decline in performance is due to random fluctuations in results. However, it would be lazy to conclude that without diving deeper.
First, let’s identify the part of Lugo’s game that’s declined the most: his ability to prevent home runs. His K%-BB% has suffered, but less so. SIERA relies heavily on K% and BB% to estimate ERA, so the .36 increase in SIERA is a good rough estimate of how much his worsened K-BB% has impacted him. Let’s see if we can figure out the source of all these home runs by making the same comparison with home run-related metrics.
| HR/9 | HR/FB% | Barrel% | GB% | LD% | IFFB% | FB% | GB/FB | |
| Dominant | 0.72 | 9.1% | 6.1% | 45.7% | 19% | 6.7% | 35.3% | 1.30 |
| Good | 1.13 | 13.2% | 7.1% | 42.8% | 22.2% | 5.9% | 35.1% | 1.22 |
Surprisingly, there is a slight decrease in Lugo’s flyball percentage from the dominant years to the good years. The main culprit of the increase in HR/9 seems to be a 4.1 percentage point increase in HR/FB%. The simplest conclusion from this is that Lugo’s lucky HR/FB% regressed to the league average. If we go back to our first table and look at xFIP—which estimates FIP with a league-average HR/FB%—there is very little change from the dominant years to the merely good years (3.44 to 3.62). There are also some changes in batted ball data, albeit slight, that will explain some of Lugo’s increase in HR/FB%. The decrease in IFFB% (the percentage of fly balls that are in the infield) certainly contributed to the HR/FB% increase at least a little, and the increases in both barrel% and line drive% also explain some of the HR/FB% increase.
After digging deeper, it doesn’t seem like Lugo has any particular skill at manipulating HR/FB% that we haven’t already covered here—there’s nothing particularly interesting about his directional sprays on fly balls or his hard-hit rate on fly balls. It appears that the best determinant of Lugo’s HR/FB% is how many barrels he allows. Look at the table below:
| Season | IP | Barrel% | HR/FB |
| 2016 | 17 | 8.90% | 0.00% |
| 2017 | 3 | 25.00% | 33.30% |
| 2018 | 78.1 | 5.80% | 7.50% |
| 2019 | 80 | 5.30% | 10.80% |
| 2020 | 10.1 | 3.70% | 16.70% |
| 2021 | 46.1 | 8.30% | 15.00% |
| 2022 | 24.1 | 5.20% | 10.7% |
If we ignore small samples (and juiced balls) in 2016, 2017, and 2020, we can see a clear connection between Lugo’s Barrel% and HR/FB%.
But Lugo’s barrel rate and HR/FB% are back down in 2022. Why isn’t the ERA down as well? Why isn’t he the dominant pitcher he used to be?
Lugo’s lowest HR/FB rates involved a significant amount of luck. In addition to limiting barrels, Lugo had to be in the good graces of the baseball gods to have a HR/FB% of 7.50% in 2018. This year, his 2022 HR/FB rate doesn’t match his 79th percentile barrel rate. Because balls aren’t carrying as much, the average HR/FB% this year is 11.0%, which is only slightly higher than Lugo’s.
So, has Lugo’s merely good 2022 been simply bad luck? No. To estimate what Lugo’s ERA should be based on his barrels, we can use Connor Kurcon’s creation pCRA, which we can find on Alex Chamberlain’s Pitch Leaderboards. Lugo’s pCRA is 3.65, which is actually higher than his 3.51 ERA.
Unfortunately, while Lugo has been able to regain his ability to prevent barrels, he has lost his ability to generate whiffs and rack up strikeouts. This year Lugo’s whiff rate and chase rate are in the ninth and third percentiles, respectively, leaving him with a pedestrian 26.9% CSW and 21.8 K%.
This begins the second half of this blog, which will cover Lugo’s whiff rate. In the first half, we discussed Lugo’s HR/FB%. However—just as Lugo seems to have done—in putting the HR/FB issue to bed, we forgot about missing bats. Just as some struggling players might watch film of themselves when they were in a groove, we’re going to revisit some excellent statistical analysis Devan Fink did on Seth Lugo in 2019. Fink explains the importance of Lugo’s fastballs and the way he tunnels them with the curveball—in short, Lugo’s fastballs are the key to him getting whiffs. Out of Lugo’s top “triad of unhittable weapons”—four-seam fastball, sinker, and curveball—the four-seamer had the highest whiff rate in 2019 with 29.5%. However, that number has dropped to 16.7% this year.
Just to check it off from the list of possible explanations, let’s make sure we’re dealing with the same pitches that Fink was three years ago. If we compare the characteristics of Lugo’s favorite three offerings in 2019 and 2022, we find little difference.
| 2019 Velocity | 2022 Velocity | 2019 Vertical Movement (inches of drop) | 2022 Vertical Movement (inches of drop) | 2019 Horizontal Movement (inches) | 2022 Horizontal Movement (inches) | |
| Four-seamer | 94.5 mph | 94.3 mph | 14.4 | 13.5 | 7.5 | 7.3 |
| Two-seamer | 94.1 mph | 94 mph | 19.2 | 18.9 | 15.8 | 15.5 |
| Curveball | 79.6 mph | 79.1 mph | 61.9 | 61.9 | 12.7 | 10.9 |
There’s virtually no difference here—Lugo still has the same toolset praised in Fink’s article. However, Fink says that pitch sequencing and tunneling—the deception of having two different pitches follow very similar trajectories before diverging—elevates Lugo’s game to the next level. Unfortunately, tunneling is a very complex concept with little publicly available data, but Brooks Baseball does provide data on the horizontal and vertical release points, which is important for tunneling.
Both graphs show a widening gap between release points starting in 2021. In the past two years, Lugo’s sinker has had a different vertical release point than his four-seam and curveball, and his curveball has had a different horizontal release point than his four-seam and sinker. If so much of Lugo’s swing-and-miss generation relied on tunneling, it makes sense that the number of whiffs on his fastball would plummet once he was no longer matching release points as well as he had been.
This analysis comes as neither good nor bad news. Fortunately, Lugo still has the same stuff he always did—if he lost several mph on his fastball or some break on his curveball, that would be a much bigger problem. However, he also isn’t just getting unlucky—there has actually been a decline in his skill. Since 2019, Lugo has increased his curveball usage by over 10% and decreased his usage on fastballs by 7.7%, so it’s likely that he has noticed that his heaters aren’t performing like they used to. Lugo isn’t going to return to his 2019 form by relying so heavily on his curveball. He can still be a good reliever because his stuff is good in a vacuum, however, to regain his dominance, he has to once again tunnel his pitches effectively.
