Why did the Diamondbacks acquire him?
Due to injuries, the Diamondbacks need pitchers. At the trade deadline, the Diamondbacks intended acquisition of Clay Holmes did not happen. Therefore, after the deadline, they were in the market for free agent pitchers. They signed Dennis Santana to a minor league contract.
Baseball Reference shows Clay Holmes on the list of ten pitchers most similar to Dennis Santana at age 29 (when Clay Holmes was a relief pitcher). Perhaps Clay Holmes and Dennis Santana have qualities that the Diamondbacks look
for when they acquire pitchers.
Despite being released, the Diamondbacks saw Dennis Santana as a pitcher whose stuff had NOT declined from the level of excellence shown last season.
This season, his Whiff Percentage improved for his slider, 4-seam fastball, and his sinker. This season, batters whiffed at 37.6% of his sliders.
This season, his Got-The-Job-Done (zero earned runs and zero inherited runners scored) was 70%, which was above my demarcation line of 67%. In other words, he performed excellently in 70% of his appearances.
Dennis Santana had experience with Jeremy Bleich (assistant GM focusing on pitching) that likely indicated that Santana was capable of change (improvement) and would be comfortable changing (improving).
Why might he improve?
Relief Pitcher Volatility. Relief pitcher performance is volatile. This season, half the Pirates relievers are better than last season (ERA+) and half are worse per Baseball Reference.
Reversability. His expected ERA (xERA) went from 3.22 (84th percentile) in 2024, to 3.51 (72nd percentile) in 2025, to 5.29 (10th percentile) in 2026 per Baseball Savant. In the absence of injury, such a large change is very likely reversable. Mike Hazen seems to think it is reversable.
“And we’re looking to make a few tweaks and see if we can’t get him back righted. He was a leverage reliever last year, and he’s still young, and his stuff didn’t decline. So we felt like it was a worthwhile shot.” — Mike Hazen
Improving from 10th percentile to 50th percentile would only be reversing about half way, but 50th percentile performance could be enough to improve the team enough to reach the playoffs.
Pitch Mix.This season he increased his percentage of 4-seam fastballs from 28.6% to 30.3%, and he increased his percentage of changeups from 6.1% to 15.0% per Baseball Savant. This season, 6 of his 8 HRs allowed were on those two pitch types (which was disproportionately large). The expected SLG was very high (.535 and .555) for those two pitches. Perhaps changing his pitch mix would increase his performance.
Why might he be called up?
Three possible reasons:
Improved To Average. If he has improved his pitching performance to at least the 50th percentile, and can improve the Diamondbacks chances to reach the playoffs.
Improved But Not Yet Average. When he reaches his opt-out date, the Diamondbacks may call-him up based on optimism that his performance will continue to improve (even if he has not yet reached the 50 th percentile performance.
“Santana has an opt-out in his deal if he’s not in the Major Leagues by a certain point. That is standard for a player of his stature because they don’t want to be caught not being on a roster when Aug. 31 rolls around and eligibility for the postseason becomes a factor.” — Steve Gilbert
Injury Replacement. If an injury happens, he may the best replacement option.
Why might he remain in the minors?
Two possible reasons:
Another Pitcher Was Signed. After they signed Dennis Santana, the Diamondbacks signed Zack Littell. In July, Zack Littell showed significant improvement, albeit one bad performance in five games. Ignoring his one bad performance, comparing July to June, his ERA improved from 4.26 to 1.37, and his home runs per 9 innings improved from 3.0 to 0.5.
With that type of performance, there is a good chance that Zack Littell will remain on the active roster for the rest of the season.
Worth noting is that although this season he averaged 4.9 innings per game, in 35% of his games he entered the game as a reliever. Perhaps he will be exclusively a long reliever, leaving room for Santana to possibly join the bullpen in a different role.
Improvement Not Seen. If the Diamondbacks do not see improvement in Dennis Santana, it is likely he will remain in the minors, even if he changes teams.
Summary.
The Diamondbacks had several good reasons to acquire Dennis Santana. He might improve as a Diamondback because relief pitcher volatility, the reversability of this season’s decline in performance, and he could change his pitch mix.
Three reasons he could be called up by 31 August are improvement to average, optimism that his performance will continue to improve at the opt-out date, and injury replacement.
