Diamondbacks Missed Opportunity to Sign Underrated Reliever

One of the stated goals for Arizona Diamondbacks GM Mike Hazen this offseason has been to upgrade the bullpen. That's understandable, as the D-backs once again had one of the worst bullpens in MLB in 2025, coming in at No. 28 according to FanGraphs rankings.

Earlier this offseason it was reported that the Arizona Diamondbacks were interested in 35-year-old right-hander Pierce Johnson. He's a pitcher the D-backs have had interest in before, and he's coming off a good season. But since the report on December 9, there has been no further movement on this front.

Another name the Diamondbacks should be kicking the tires on is free agent right-hander Shawn Armstrong. He is also 35 years old, and is quite comparable to Johnson in many ways. They have very similar career numbers, although the last three seasons in aggregate favor Armstrong.

The Case for Shawn Armstrong

Armstrong began his professional career in the Cleveland Guardians' organization following the 2011 draft. He's bounced around to 11 different teams during his career. Over 370 games, 421 innings pitched he's compiled a 3.82 ERA and 3.70 FIP, along with 4.6 FangGraphs WAR and 4.0 Baseball-Reference WAR.

His best two seasons came in 2023 for the Tampa Bay Rays and 2025 for the Texas Rangers. Those seasons were sandwiched around a poor season in 2024 in which he pitched for three different teams. That illustrates the volatile nature of reliever results.

The table below shows his last three seasons' ERA, FIP (Fielding Independent Pitching from FanGraphs) and xERA (Expected ERA from Statcast).

Overall, those are very solid results the last three years, the average of which would represent a major upgrade to the Diamondbacks bullpen.

It's notable that Armstrong was given a career-high number of chances in high leverage outings (24) and posted the highest leverage index of his career at 1.28 (MLB Average leverage is 1.00).

He recorded nine saves and had three blown saves, but all three of those were in the sixth or seventh inning. He converted all six of his ninth-inning or later chances, and also had three multi-inning saves where he entered in the eighth inning.

Armstrong featured a very balanced four-pitch mix in 2025, throwing 29% four-seam fastballs, 24% cutters, 23.5% sinkers, and 23.4% sweepers. The fastball averages 93.5-94 MPH, and both the sweeper and four-seamer generated 34% whiff rates — leading to a well-above-average 26% strikeout rate and 7% walk rate.

Perhaps most notably, Armstrong has been very adept at limiting the long ball the last several years. Since 2023, among relievers with at least 150 innings thrown, his home run per fly ball rate of 5.9% ranks the third lowest in the majors. His HR/9 rate of 0.66 ranks 13th.

That can be viewed as both a feature and a bug of course, as some regression to the mean in this category could be expected. But his expected home runs per Statcast the last three seasons were just 14.7, versus 13 actual homers allowed. Furthermore, Chase Field is one of the tougher parks in MLB to homer at according to Statcast Park Factors, especially for left-hand batters.

The Case Against Shawn Armstrong

There isn't much of one, outside of his age, cost, and the volatile nature of relievers to begin with. His poor 2024 season is a caution flag perhaps.

While FanGraphs' crowdsourcing pegged his estimated contract at one year, $4.5 million, that is almost certainly too low. Based on how the reliever market has actually played out this offseason, relievers that had estimates attached to them have beat those estimates by about 24% on average.

But the mid-tier relievers such as Brad Keller, Luke Weaver, Tyler Rogers, Phil Maton, etc have all done even much better than that. Based on the market to date, the estimate for Armstrong would likely be in the $6-8 million range.

Summary

Shawn Armstrong is a four-pitch reliever with some excellent peripherals and high-leverage track record in his most recent past. His velocity has not dipped and he's been durable the last several seasons.

He might cost the Diamondbacks around $6-8 million, but the team cannot afford to pass on chances to bolster their bullpen. If they cannot fit this type of contract into their budget, they will be forced to give up top-ranked prospects to upgrade the bullpen, which is never a first choice.

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