The Astros at Memorial Day. Theme #2: The Bullpen Has Been Great

The Astros bullpen is 2nd in the majors in ERA. They had done it by identifying promising pitchers off of the scrap heap and developing them into effective pitchers.

On Saturday, the Astros held a scant one-run lead when Framber Valdez handed the ball over to the bullpen. The offense did not score again, so the bullpen was required to hold the line with no mistakes to bring home a win.

The combination of Bennett Sousa, Bryan Abreu, and Josh Hader each threw an inning, and collectively allowed only 1 hit and 1 walk while striking out six Mariners hitters. Thanks to the work of the bullpen, the lead was never in doubt.

That should not be surprising at this point in the season. The Astros bullpen has been the backbone of the 2025 team.

Astros relievers have been excellent all season, among the handful of best bullpens in the majors. You can see the evidence for that claim in the table below, which shows some of the key numbers for the Astros bullpen and their rank among major league teams.

Astros relievers have the second-best ERA of any bullpen in baseball. The other numbers in the table show that the bullpen’s excellent ERA is not a mirage. Astros relievers are top 3 in the majors in Fielding Independent Pitching, strikeout rate, (K%) opponent batting average, and barrel rate allowed. The are fourth best in WHIP, fifth best in K% minus BB%, and sixth best in hard hit rate allowed.

The only measure where the Astros bullpen has been middle tier is in walk rate. They are ranked 17th in that measure. This should not be surprising; Astros pitchers have run high walk rates over the last several seasons but have combined that with a high strikeout rate and low batting average to be a strong run prevention unit. The 2025 bullpen is following in that path.

A Deep Bullpen

For a team to have an excellent bullpen requires not just the high leverage relievers to pitch well, but good performances from a wide range of pitchers. That is what the Astros have received this season. Their bullpen has been anchored by excellent performances by their top two relievers in Josh Hader and Bryan Abreu but have also received great performances by a wide variety of relievers.

The chart below shows the ERA for the eight Astros relievers who have an ERA under 2.50.¹ That’s a whole bullpen’s worth of relievers, and all are doing their job. They are making it very hard for opposing hitters to come around to score.

Like most teams, the Astros have sorted through a number of options in their bullpen so far this season. But almost everyone of them has worked out. The Astros have employed 13 relievers this season and 8 have been outstanding. Furthermore, this list includes 7 of the 8 relievers who have thrown the most innings for the team so far this season.

The Change In Bullpen Philosophy is Working

I have written several times over the last few seasons about how the Astros have changed philosophies on how to build their bullpen. Across the Golden Era, the Astros front office has put a great deal of their resources in trade assets and free agent dollars into their bullpen. That has changed over the last two seasons, as the team has shifted to sorting through a number of scrap heap options to identify ones that can work.

The change is philosophy was best exemplified this offseason, when the Astros traded Ryan Pressly to the Cubs in an effort to avoid paying the luxury tax. And while trading Pressly turned out to be addition by subtraction (Pressly has a 5.40 ERA in Chicago with 10 strikeouts and 9 walks in 18 innings pitched). But, as Chandler Rome of The Athletic wrote in a Spring Training preview, it “deprived the bullpen of a durable veteran familiar with every sort of sticky situation.”

It turns out familiarity is overrated and strikeout rate is underrated. The Astros were able to build a bullpen of unfamiliar names who came essentially out of nowhere to be productive. Bryan King was acquired in the minor league portion of the Rule 5 draft. Steven Okert was signed as a minor league free agent after a bad season with the Twins in 2024. Kaleb Ort and Bennet Sousa were waived claims by the Astros. Guston and Dubin were late round draft picks by the Astros (11th and 13th rounds respectively).

In short, any team in the majors could have had these pitchers. In fact, several other teams did have some of these pitchers, but could not get the best out of them.

That the Astros are is another piece of evidence of the effectiveness of the team’s pitching development system, headed by pitching coaches Josh Miller and Bill Murphy. I wrote about their excellent performance in 2024 last August, identifying them as the 2024 Astros MVPs. They will have another case for the award this season, thanks to their excellent work with so many scrap heap relievers.

A common sight for Astros fans in 2025. An Astros reliever (in this case Kaleb Ort), receiving a hand shake from his catcher congratulating him on closing out a win.

To give an example of how this works, take Kaleb Ort. Ort reached AAA in 2019 and bounced around between AAA and the majors across three organizations from then until Spring 2024. Between the Yankees, Red Sox and Orioles, Ort threw 193 innings between 2019 and 2024 at AAA and in the majors, walking nearly 12% of the batters he faced. It led to a 4.56 ERA for Ort, an inability to stick in the majors and 4 DFAs.

The Astros claimed Ort off of waivers in May 2024 and immediately helped him get his walks under control in a stint in Sugar Land. That led to a mid-season call up where Ort was excellent; he walked only 4 batters in 24 major league innings last year.

In 58 innings in the Astros organization, Ort has gotten his walk rate down to 8.6%, while maintaining an above average strikeout rate of 26.6%. Others couldn’t get the best out of Kaleb Ort, but the Astros did and they are reaping the benefits of their work.

Bigger Challenges Ahead

An additional bit of good news for the Astros bullpen is that they have not been overworked so far this season. They have collectively thrown 179 innings, which is the 19th highest in the majors.

They are likely to have to take a higher burden moving forward. The starting rotation will be compromised the rest of the season. Hayden Wesneski is out for the season with Tommy John surgery. Ronel Blanco was recently placed on the IL with elbow soreness and is seeking a second opinion, which means he did not like the first opinion. Spencer Arrighetti is still recovering from a broken finger. Lance McCullers seems unlikely to return to being a workhorse in his return from his own elbow surgery, and the rehabilitation of Luis Garcia’s elbow seems to be going slowly.

This has forced the Astros to rely on rookies such as Colton Gordon in their rotation. The team has also moved Gusto out of the bullpen and into the starting rotation.

The bullpen is thus likely to be called upon for a higher share of the team’s innings over the final two-thirds of the season than they were in the first. This will put more stress on the pen. At one level, they will certainly regress to the mean. It would be great to get a 2.86 ERA over the entire season from the bullpen, but that is unrealistic.

But the excellent performance so far this season—highlighted by the bullpen’s strong strikeout rate—gives lots of reasons for optimism. This has been a really good bullpen. We will need it to continue that moving forward.

1. Ryan Gusto’s numbers in the chart are from his bullpen work only. I separated out his numbers as a starter.