Can Trevor Stephan be Fixed?

In the first year of his five-year contract extension with the Guardians, Trevor Stephan’s performance was uneven, to put it lightly, in the role of set-up man for closer Emmanuel Clase. Can Stephan return to the effectiveness he showed in 2022?

First, let’s review the stats. In 2022, Trevor Stephan had a 2.69 ERA, a 2.34 xERA, a 2.19 FIP, and a 2.81 xFIP, with a 11.59/2.54 K/BB/9. In 2023, Stephan had a 4.06 ERA, a 4.51 xERA, a 3.56 FIP, a 4.26 xFIP, with a 9.83/3.41 K/BB/9. The decline in performance is pretty clearly captured here, moving Stephan from a pitcher you’re happy to see in the eighth inning of a tie game to someone you’d be fine seeing in the sixth inning when you have a three-run lead. Obviously, the Guardians didn’t sign him to 4 year, $10M contract with two club options for 2027-2028 hoping he would be the latter.

To begin the process of analyzing what is wrong with Stephan, I’d like to throw out one obvious observation. Since 2021, Stephan is 35th in appearances among 1259 major league pitchers who have thrown at least one pitch in relief. Stephan may be tired... or, his body may also be getting used to the grind of 60+ appearances, year-in and year-out.

Now, I will note that the month in which Stephan threw the most innings in 2023 was August (13) was also his best month in performance by far (2.48 FIP, 11.77/1.38 K/BB/9). Stephan did have eight back-to-back appearances from Opening Day until July 31st and only one back-to-back appearance in August, so it’s theoretically possible that the team (and Tito) decided he would increase his effectiveness if he were not asked to do back-to-back appearances.

However, Stephan only gave up runs in the second of back-to-back appearances twice out of the 10 times he did it in 2023, so I don’t think there’s strong evidence that his issues were mostly related to overuse. We can hope that another offseason of work and conditioning can help Stephan regain his 2022 form with some additional endurance built up through the hard experience of 2023, but the numbers don’t necessarily indicate that this is more than a piece of fan optimism.

What do the numbers show, then? Declines in velocity across the board, as his four-seamer went down by 1.7 mph in average speed, his split finger declined by 1.4 mph and his slider declined by 0.4 mph. His decline in pitch command is also obvious, with an increase in walk rate of 0.9 walks per 9, If you look at his breakdowns by pitch type, Stephan threw 30.8% of his sliders for balls in 2022 and 34.8% of them for balls in 2022, 41.9% of his splits for balls in 2022 to 43% in 2023, and 30.9% of his four-seamers for balls in 2022 to 34.7% in 2023. The combined 8% jump in number of balls on sliders and four-seamers seems to be a pretty clear sign of what went wrong for Stephan in 2023.

Run value-wise, Stephan went from 1.3 runs above average on his four-seamer in 2022 to 3 runs above average on it in 2023, stayed steady at around 2 runs above average on his split finger, but went from 3.9 runs above average on his slider in 2022 to -1 run below average on it in 2023. Put in another way, his wOBA allowed on sliders went from .243 in 2022 to .371 in 2023. Hitters, in general, were either taking his sliders for balls or hitting them hard in 2023.

So, fix the slider, and everything else will follow, right? Not necessarily, as the decline in velocity for both Stephan’s four-seamer and his split lessened the separation in velocity he is normally able to achieve for both of those pitches. This allows the hitter to more easily adjust to wait back on a slider in a situation in which he is also protecting against a fastball. So, while Stephan’s fastball and split, themselves, may have still been just as, if not more, effective while down about a mile and to a mile and a half per hour in velocity, that decline may be having a negative impact on his secondary stuff.

Speaking of other pitches impacting the slider, when we open up Stephan’s Baseball Savant page, we will notice fairly significant declines in the horizontal movement of both his split and his four-seamer...

...but Stephan’s slider is more of a drop slider than a sweeper, so horizontal movement on the slider isn’t as important. While the decline of horizontal movement on his split and fastball may be allowing hitters to stay off of them and gear up for the slider, the even more troubling sign is the DRAMATIC decline in the vertical movement of his split-finger AND slider from 2022 to 2023.

These are Stephan’s out-pitches and they were not functioning that way in 2023. While the split-finger remains an effective pitch for Stephan, it’s fair to wonder if it now essentially lacks significant difference in shape and movement from his slider, leading hitters to be able to more quickly identify Stephan’s third pitch and either take it or hit it a country mile.

If you look at clips, it’s not hard to see the difference between Stephan’s 2022 slider and his 2023 slider. Here’s Stephan fooling Aaron Judge in the ALDS in October of 2022:

To this hard-hit ball by Donovan Solano in September of 2023

You can see that the slider isn’t dropping as much, and it’s also tailing toward instead of away from the hitter. If you go and look at sliders from Stephan in 2022 and 2023, you’ll notice this is a pattern.

So, what does Stephan need to do to address these issues?

One, work on his slider shape, try to recapture some of that good vertical movement from 2022, while also addressing the similar decline in vertical movement on his split-finger. In talking to our site editor/head writer Matt Dallas about this piece, Matt reminded me that it’s a generally observed trend that split-heavy pitchers tend to see decline in overall pitch velocity. It’s still worth seeing if Stephan can find some of that missing velo, something his splitfinger-mentor Bryan Shaw has done fairly often in between seasons.

Second, identify some offseason strength and conditioning work to see if he can regain and maintain a few ticks on velocity for all of his pitches.

Third, Stephan may want to address his pitch mix in hopes of keeping hitters off of his slider. After learning to throw his split-finger in 2021, Stephan has been consistently around 47% with his four-seamer, 28% with his split, and 25% with his slider. I wonder if it would be possible to adjust his slider usage to more of once every five pitches instead of once every four pitches, focusing on quality over quantity. He can then allocate that extra 5-10% of pitches to throwing more split fingers in the lower part of the zone. I’m a fan of Stephan putting even more trust in a split-finger pitch he has now leaned on for a .212 wOBA and a 47% K-rate in 2023 and a .206 wOBA and a 54.7% K-rate in 2022. If the split, which is a great pitch for Stephan, is affecting his overall velo, as Matt Dallas suggests, it may make some sense to place more eggs in the split basket to focus on increasing its effectiveness above all else.

There’s no skirting around the fact that there are some warning signs with Trevor Stephan, with his 2023 numbers looking spookily similar to his 2021 numbers, and his 2022 season, thus, looking like the outlier. I remain optimistic, however, that a player who taught himself a new, effective pitch in the split-finger at the major league level can work with the Guardians’ coaching and catching staff to fix the issues he ran into in 2023, rediscover a good portion of his 2022 effectiveness, and solidify the backend of the Guardians bullpen. I’m hopeful that the team’s extending of a contract to Stephan indicated their belief in his ability to adapt and endure while making the constant adjustments necessary to be a valuable big league reliever. Now, it’s just up to him to prove it.