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Looking for Free Agent Relievers

Screening for Pitchers with the Right Stuff

MLB: ALCS-Houston Astros at Texas Rangers
Astros’ reliever Ryan Pressly in game 5 of the ALCS has the right stuff.
Kevin Jairaj-USA TODAY Sports

It’s no secret that the Astros’ off-season plans will include relief pitcher acquisition. Three relievers on the 2023 team will be free agents: Hector Neris, Phil Maton, and Ryne Stanek. Maybe the Astros could muster an internal replacement for one or two of these pitchers, but likely not all three. External acquistions can occur through either trade or free agent signing. Since I don’t have any inside knowledge of trades which the Astros might consider, this article will focus on the free agent market.

In previous articles I screened LH LF free agents and catcher free agents, so that I could identify the most promising free agents to meet the Astros’ needs. How should I screen the relief pitchers? In this article, I will identify relievers with a high Stuff+ rating in 2023. In my view, pure Stuff is the most important characteristic of a high leverage reliever. Other stats, like ERA, WHIP, and FIP are useful, but there are limitations on interpreting or applying them to a reliever’s future performance. Relief pitcher stats are more sensitive to sample size issues, BABIP volatility, good/bad luck, and the manner in which the reliever was used by his previous team.

But a pitchers’ Stuff+ is based on the physical characteristics of the pitches. It’s the physical foundation of the relief pitcher’s performance, regardless of sample size or luck questions. Pure stuff is what allows a reliever to be dominant. And the Astros have been very successful over the last two years in building a bullpen based on very good stuff. In both 2023 and 2022, the Astros’ bullpen was the MLB’s No. 1 team in Stuff+ . People like to complain about Astros’ closer Ryan Pressly. (Well, all teams’ fans like to complain about their closer.) But Pressly is No. 1 among all MLB relievers in Stuff+. (Pressly: Stuff+ of 156, with 100 as average stuff.) Bryan Abreu is No. 8 in Stuff+ among all MLB relievers (139 Stuff+). That’s impressive. The Astros’ closer and set up man are No. 1 and No. 8 in the stuff they bring to the mound.

The list below is based on free agent relievers with appealing performance, but more importantly a high Stuff+ rating. Like my previous articles, I have used the Fangraphs’ free agent tracker, which includes a crowd source estimate of likely contract amounts and lengths.

  1. Aroldis Chapman (Stuff+ 134). I can already hear fans complaining about this listing before I have even pushed the publish button. The lefty closer has been a frequent foe in playoff games over the past few years, and many Astros’ fans don’t like him. But this exercise isn’t about subjective likeability. Chapman has undeniably good stuff. He throws a 100 mph sinker with a Stuff+ of 177. His split finger pitch has a Stuff+ of 181, and his 104 mph fastball has a Stuff+ of 125. (And his 2.84 x-ERA is lower than his actual 3.09 ERA.) Yes, his control can be erratic. He seems to turn many 9th innings into a high wire act. But adding him to the Pressley-Abreu equation would create an imposing wall of stuff in the Astros’ late innings. And the Cuban flame-thrower would join a team with two of the most respected Cuban baseball players, Yordan Alvarez and Jose Abreu. Maybe that would be a good influence on Chapman. If the crowd source estimate is correct—$7.5 M X 1 year—that is likely to be a bargain.
  2. Dave Robertson (Stuff+ 125). Robertson’s top pitches are a cutter, slider, and knuckle curve. He has considerable experience in late inning high leverage work. Robertson’s x-ERA and ERA are 3.23 and 3.03, respectively, but his FIP runs into the 4’s, not unlike many high leverage relievers. The projection systems suggest some degree of regression (closer to his FIP) in 2024, which is certainly a risk at his age (38). The crowd source salary is $8 M x 1 year.
  3. Craig Kimbrel (Stuff+ 125). Kimbrel has a lengthy career as one of the most dominant closers in baseball, but his fearsomeness seems to have receded a bit with age. Kimbrel’s two main pitches are a 96/97 fastball and a knuckle curve, both of which rate about equally well with Stuff+. The crowd source estimate is 1 X $10 million, which may be a little expensive for the Astros. At age 36, that salary may be over valuing what he can provide in the late innings.
  4. Jordan Hicks (Stuff+ 125). Hicks is a 27 year old hard thrower (100 mph average velocity) who features a plus fastball, plus slider, and plus change up. He strike out more than 11 per 9 innings, but also walks more than 4 per 9 innings. His stuff is so good that one might hope that he develops into a dominant reliever, but it’s also easy to imagine that he will have a career path similar to Ryne Stanek. Both his actual and x-ERA, as well as the projections, see Hicks as a 3.30-ish ERA performer. Although his stats look pretty good in 2023, he still had some rocky moments (as indicated by 13 meltdowns). The crowd source estimate is 3 years, $27 million. The AAV isn’t that bad, but a three year contract for a reliever may carry more risk than the Astros will want to pay.
  5. Robert Stephenson (Stuff+ 116). Stuff+ likes Stephenson’s 97 mph fastball and plus slider. He has a very good 13 K/9 and 2.75 BB/9. He pitched 52 innings of 3-ish ERA ball for the Rays at a salary of $1.8 million. His 2.73 x-ERA is below his actual ERA of 3.10, which may be a sign that he will resist regression. (A September Fangraphs articles lists him as one of the most under rated players on the Tampa Bay Rays.) Crowd sourcing expects 2 years at $5 million per year. At this price, he would a reasonable target for the Astros.
  6. Jake Diekman (Stuff+ 141). Diekman has been used as a lefty specialist most of his career. The 36 year old posted one of his best ERA seasons (3.34). And his Stuff+ ratings were exceptional. Stuff+ particularly likes his fastball and slider (164 and 140, respectively). While Diekman’s K rate is good (10 K/9), the walk rate is not so great (6 BB/9). Crowd source does not provide an estimate for his contract. But his current salary is $4 million per year.
  7. Colin McHugh (Stuff+ 113). He is an Astros’ fan favorite from his days as an Astros starting pitcher. Stuff+ rates McHugh’s slider at 125. He is primarily a cutter / slider pitcher who occasionally mixes in a curve ball. The risk factor: McHugh was shut down with a shoulder injury late in the season. Obviously, the Astros would need to examine his medicals carefully. McHugh’s results were sub par in 2023, ending the season with a 4-ish ERA; but his stuff remained above average. The crowd source contract estimate is 1 year, $3 million.
  8. Josh Hader (Stuff+112). Hader, the former Astros’ farm hand, has a reputation as a dominant LH closer. Given his reputation, Hader will probably receive a richer contract than the Astros can offer. (However, it is rumored that the Astros showed interest in Hader at the 2023 mid-season trade deadline.) His Stuff+ rating is quite good, but not in the elite category. Perhaps this is because Stuff+ does not measure deception, which is a significant part of Hader’s delivery. His best pitches are a sinker and slider. The crowd source contract is 4 years, $78 million, with an $18 million AAV. This likely exceeds the Astros’ financial limitations, and as much as I like this pitcher, that amount probably over-values what the reliever’s performance can add to the team.
  9. Shelby Miller (Stuff+ 111). The 33 year old Miller throws a fastball, split finger, and slider, which are all above average, according to Stuff+. The split-finger pitch exhibits the best stuff (124 Stuff+). Miller pitched 42 innings for the Dodgers, posting a 1.71 ERA with a 3.38 x-ERA. Beware, though, that the projections suggest that the ERA could regress into a 4-ish range. As a former starter, Miller can be used as an opener or tandem starter, if needed. He is currently paid $1.5 million/year.


The best free agent choices depends on how much the Astros are willing to spend. Reportedly, the Astros may be $9 - $10 million below the luxury tax threshold. If the Astros decide they won’t cross that threshold, the team is probably constrained to the cheapest options (perhaps Shelby Miller or Colin McHugh). If the Astros decide to show a little more leniency to exceed the threshold, perhaps the relief pitchers in the $8 - $10 million range are feasible.

My personal preference is either Aroldis Chapman or Robert Stephenson, assuming the crowd sourcing estimates are roughly accurate. Either pitcher would add a dominant strike out pitcher behind Pressly and Abreu. Opposing hitters certainly would not look forward to the stuff they would face in the last three innings of the game.

Notice that I have not addressed the option of re-signing the three Astros’ free agent pitchers. The crowd source estimate for Neris is 2 years, $16 million ($8 million AAV). At $8 million/year, Neris costs the same as a pitcher like David Robertson. And it’s possible that Neris’ affinity with the team would lead the Astros to favor Neris over a pitcher like Robertson. However, Neris’ stuff appears to be inferior to these free agent pitchers (Neris Stuff+ 99). Neris posted an outstanding 2023 season, in terms of ERA and RE24. However, the odds would seem to favor some level of regression from the extremely good numbers posted in 2023.

Among the departing pitchers, Ryne Stanek exhibits the best Stuff+ rating at 131. Stanek’s stuff is ranked higher than Jordan Hicks, for instance, but most likely Stanek will receive a substantially lower salary in free agency than Hicks. At the right price, it may make sense for the Astros to retain Stanek. Phil Maton has a 100 Stuff+ rating, which suggests that he is an average relief pitcher. His current salary is $2.6 million. Would the Astros re-sign him if he accepted something close to his current salary? Or would the Astros be better off replacing him with reliever at a cost controlled salary (such Seth Martinez)? Those are the kinds of questions the Astros will have to contemplate.