How An Arm Slot Change Might Have Saved Yu Darvish's Season

[Randy Holt]

The San Diego Padres waited roughly three months for the 2025 debut of starting pitcher Yu Darvish. While the timeline wasn't ideal, the timing of his return was. Down Michael King in a thinning — and some cases struggling — rotation, the team was likely hoping that the veteran would offer some stability upon his return. That, of course, didn't happen out of the gate. 

In his first start on July 7th, Darvish was unable to work through the fourth inning. He allowed a pair of earned runs (three overall) while striking out five and walking three in 3 2/3 innings. There wasn't anything especially concerning there, with the assumption being that start-to-start longevity would require additional building up. In his next two starts, though, Darvish threw a combined 9 2/3 innings, allowed seven earned runs, and only struck out three hitters. That started to ignite some concern as to whether he'd be remotely reliable moving forward, let alone bring that craved stability. 

Questions were further amplified in start number four. Against the St. Louis Cardinals on July 24th, Darvish was again unable to escape the fourth inning. He allowed an obscene eight earned runs in a start that included eight hits, two walks, and a pair of home runs. But then something kind of fascinating happened: Darvish suddenly became effective.

Darvish's next outing came against the New York Mets on July 30th. In that start, he worked seven full innings, surrendered just two hits, and struck out seven without walking a hitter. He wasn't quite able to replicate the same success in his most recent start on August 5th, but he did strike out five and allow just three hits across four innings (one of which happened to be a home run). The two starts worked together to reignite a little bit of optimism that Darvish could be more of an asset than a detriment as we creep toward the season's final stretch. 

Notably, Darvish attributed the increased success following the start against the Mets to a decreased arm angle. Regardless of the difference in outcomes, it's now a trend we've seen in each of his last two starts: 

As an aside, any graph illustrating individual pitches from Darvish is going to look much more overwhelming due to the volume of pitch types he throws. But focusing on the arm slot component, the most notable decline in that respect took place between his start on July 24th and the one on July 30th. The arm slot declined further between that excellent Mets start and his most recent effort against the Arizona Diamondbacks earlier this week. Even through all the various colors, the slot drop is extremely evident. 

Darvish's arm slot in his first start off the Injured List checked in at 43.3 degrees. He hadn't had an arm slot that steep since 2021. It leveled out a bit in the three subsequent starts, coming in at 39.9 degrees in the July 24th start. From there, though, he dropped it to 32.7 against the Mets and 28.3 against the Diamondbacks. There's likely going to be a medium into which he settles moving forward, but it's a precipitous drop in his arm angle from what we saw immediately upon his return.

In the stretch before the arm slot drop (four starts), Darvish's numbers read 16 2/3 innings, 11 strikeouts, nine walks, and a 9.91 ERA. In the two since, he's gone 11 innings, 12 strikeouts, two walks, and a 3.38 ERA. His Whiff% checks in at 28.3 in the two more recent starts, while his hard hit rate against has averaged 28.5 percent.

There are a couple of caveats within that, of course. You're looking at an imbalanced comparison between a set of four starts and just two. And one of those two starts is working to prop up the numbers. Ultimately, though, there have been strong signs of increased effectiveness for Darvish in the two starts since he dropped the arm slot. Plus, there's this: 

In dropping the arm slot, Darvish has been able to get back to what makes him most effective: whiffs. He's parlayed that new slot into a lot more swing-and-miss than he'd been demonstrating in the four previous starts. There have been some positive movement changes helping on that front, depending on the pitch type, too. But that's not necessarily all this is about. For Darvish, it's about command.

While whiffs can be a natural byproduct of command, Darvish needs to be accurate to the zone in order to be effective. Anecdotally, his periods of struggle generally occur when he's trying to be too fine with the zone and often misses opportunities for strikes. When he has his command on point, he's able to get both called strikes and swings that feature soft contact or an outright whiff. 

We've seen flashes of it in those last two starts. The outing against the Mets, in particular, saw his contact quality plummet and, specifically, the in-zone whiff rate rise. That's the version of Yu Darvish the Padres want to see. The arm slot isn't about movement in the way that it might be for other pitchers. The nature of Darvish is that his pitches are going to move regardless of slot. Instead, his focus needs to be on efficiency. 

A two-start sample isn't enough to show us that the new arm slot is working, especially when there is still some variance in the slot itself between the pair of outings. The hope, though, is that this serves as a springboard for Darvish to harness his efficiency and, as such, his effectiveness in a rotation that needs quite a bit of both.

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