Is Jeremiah Estrada's Usage Change Eroding His Reliability in Shaky Second Half?

No team has received more value out of their bullpen than the San Diego Padres. Their 6.9 fWAR from the group is tops in the league by a wide margin, while the relief corps sits first in ERA (3.09), first in FIP (3.57), fourth in K% (25.0 percent), and third in hard hit rate against (37.6 percent). That they've done so, especially in regard to the WAR figure, while throwing just the 10th-most innings among their Major League counterparts speaks to how impressive the group has been. 

Jeremiah Estrada has been a central fixture in all of that. He ranks 32nd among qualifying relievers in fWAR (1.2), mostly due to the fact that he currently sits seventh in strikeout rate (34.9 percent). While it hasn't been quite on par with his breakout 2024 campaign, it's hard to deny his place among the game's highest-upside relievers. The percentile rankings help to illustrate just that:

The above visual is indicative of Estrada's stuff, above all. At the same time, there are a handful of second half developments that have called Estrada's value to this relief group into question, especially when one examines some of the shortcomings present in said visual. The following is where Estrada lands, statistically, in each half to date: 

• 1st Half: 43.0 IP, 2.93 ERA, 3.12 FIP, 33.5 K%, 8.9 BB%, .278 wOBA
• 2nd Half: 22.2 IP, 4.37 ERA, 3.36 FIP, 38.9 K%, 8.4 BB%, .316 wOBA

We're obviously only working with a sample about half the size thus far in half No. 2, but the ERA, in particular stands out. That figure is mostly wrought by a pair of brutal outings, including a loss to the Los Angeles Dodgers back on August 24, and a shaky win in Colorado on September 6. The latter contest was one the Padres led 10-2 but had to squeeze out by a much narrower 10-8 margin. 

Ultimately, there are some things Estrada has done well in the second half. Unlike the ERA figure, his FIP indicates that he's only been marginally worse overall while posting strikeout and walk numbers that are each actually better than what he turned in in the first half. There is, however, one primary reason to worry that we may not be through the shaky outings as we move into the middle of September:

After his best contact month in August, Estrada has seen the quality of contact against skyrocket in the second half. It's a bit of a paradox, as he's seen the K% increase steadily over that same timeframe, with September representing his highest mark in an individual month (50.0 percent). But, while the punchouts are on the rise, we have the above visual to reckon with, in addition to what the expected metrics have to say: 

At .115, his xwOBA against peaked (as in, was at its best) on August 15. In the month since, it's been steadily on the rise. Our first question is, of course, why?

Usage, in itself, does offer a likely explanation. Throughout the year, the four-seam fastball has represented Estrada's most utilized pitch. In the first handful of months, he was throwing the pitch at or just under 60 percent of the time, with his split-change hybrid serving as his secondary offering. The slider that had served that role in previous seasons took a back seat to the other two. Since the start of August, however, we've seen the four-seam and splitter usage dip while the slider has taken over. 

In August, Estrada threw his fastball 50 percent of the time. Thus far in September, it's at just 45.3 percent. The splitter, meanwhile, has dropped by five percent over the last three months, currently sitting at just 20.9 percent. In between, the slider has seen an increased role in his arsenal, rising from 13.2 percent usage in July to 33.7 percent in September. The issue is that the slider hasn't been a particularly consistent pitch since its increase. 

In August, it was responsible for the highest amount of swing-and-miss. But, it also had a .475 xwOBA against. The results haven't been there in September, as the four-seam has actually checked in higher on the whiff side. The slider has also seen a 50.0 Hard-Hit% in each of the last two months. The reason for the change remains unclear; it's possible that the grip of his split-change pitch might be cumbersome over the course of a full season, but that's purely speculation. It's also not one that has yielded pure benefits. Instead, it's led to more variability in Estrada's game.

That feeds directly into a second question around whether it's something we should be worried about moving forward, especially in a now-depleted bullpen that is without Jason Adam for the remainder of the year. 

It's somewhat unusual for a pitcher to change usage so drastically at this point in a season. Estrada's slider has been an effective pitch for him in the past, but the way the fastball-splitter combination played at the beginning of the year was indicative of a positive evolution in his toolbox. The reintroduction of the slider to this extent appears to be almost directly responsible for the paradox in which Estrada is currently living. It's getting him more whiff, yes. But, when it gets touched, it's getting touched up. 

It'll certainly be interesting to see what shape his usage takes moving forward. He's clearly dedicated to implementing that slider with more regularity. But should it be coming at the expense of the splitter, given where results have landed for that pitch? In either case, it's necessity that Estrada gets himself—and his pitch mix—sorted. Adam's absence means that Estrada is as essential as ever. The Padres can't have such a crucial arm in-between pitches as the postseason creeps ever closer.