2025 stats: 65.2 IP, 21 G (10 GS), 4.80 ERA / 4.96 FIP, 1.492 WHIP, 22.8 K%, 12.4 BB%, 0.0 fWAR
Some of us will spend most of this offseason wondering what happened to Hayden Birdsong. It’s not just that the 6’4” 23-year old who captured hearts and minds last season only to lay a big ol’ egg this season, it’s that his spiral has been so expansive and destructive that he shouldn’t be considered part of the team’s plans for 2026…
At least in the rotation.
After a heckuva spring (0.75 ERA in 12 IP — just
1 start), a glut of stronger arms in the starting rotation pushed him to the bullpen, where he wound up being mostly good and sometimes excellent. He ended April with a 1.13 ERA in 16 IP (7 games; only 1 of which was a single inning). Now, reliever ERAs in a small sample can be misleading, which is why FIP is so helpful. A 3.01 FIP isn’t as dominant as the ERA, but it put him just below the elite relievers in the sport, which gave the Giants a nice problem to have until Justin Verlander landed on the IL. That pushed Birdsong back into the rotation and it was from this point on that his interesting yet fragile season cracked.
Walks have always been a problem for the kid, along with the home run ball. Both wound up sinking his 2024, too, as you’ll recall. His final 10 appearances for the Giants came as a starter, and in those 42.1 IP he walked 27 (13.7%) and allowed 6 home runs. It worked out to a 6.17 ERA and 4.72 FIP. His fastball velocity declined, too. That four-seamer was his worst pitch last season (.529 expected slugging%), and this year, it was simply one of many that garnered ugly results.
Four-seamer: .458 xSLG
Slider: .419 xSLG
Changeup: .342 xSLG
Curveball: .393 xSLG
Slurve: 1.460 xSLG
Now, caveat: the slurve was thrown just 21 times. Meanwhile, you might wonder why he threw his four-seamer the most (44.1%) with such terrible results. Well, in some ways, the results were actually better compared to last season — lower batting average and expected slugging against, lower average exit velocity, increased whiff rate and higher spin rate, all while maintaining average velocity (95+), improved Stuff+ (95 compared to 80) — and when you look at the rest of his arsenal, then it seems as though he leaned on the pitch to bail himself out.
His slider, changeup, and curveball were all down in terms of stuff and overall his location was even worse this season. So, declined stuff on the secondary pitches coupled with bad command and there you have it: a reliever in the making. It’s perhaps not what the Giants have in mind and given his age it’s likely they’ll give him another shot at starting, but they have a lot of data for him in a starting role. After being sent to down to Sacramento, he sported a 6.69 ERA in 10 starts (39 IP) with a 9.7 H/9, 6.9 BB/9, 2.1 HR/9 and 10.8 K/9. A 1.85 WHIP is, uh, not good.
In last season’s review, our Steven Kennedy wrote:
Maybe this is wishful thinking, drawn forth by proximity and association, but I think Birdsong can be compared to starters like Snell or Ray. His stuff stuffs. We’ve already seen it overwhelm hitters. His 7.1 H/9 is up there with the best rates in the league while his 11 K/9 is much closer to Snell’s than other Giants starters.
Now, I don’t think Steven was wrong at all. The stuff plays… in short bursts. I think his alarming jump in H/9 is plausibly attributable to the Giants’ defense being porous. They were 21st in hits allowed (1,353) which wound up being 8.5 H/9. I’ll admit that, last season, the Giants were also 21st in hits allowed (8.4), but as I’ve already noted, Birdsong’s stuff wasn’t as sharp this season.
So have the Giants mis-developed Birdsong? Was putting him in the bullpen then pushing him back into the rotation a mistake? Is this a mental hiccup that can be ironed out? One of the reasons why I was rooting for Birdsong after last season is because he had the ass a la Madison Bumgarner — or, less problematically, Ryan Vogelsong. That’s valuable for a scrappy team like the Giants.
Maybe I was too quick to make a 1:1 comparison between a player today and a player from the championship era. This is a new, undefined era where the Giants are still looking for a personality. A 23-year old in the wilderness after taking his licks at the major league level is nothing new. The task ahead for Buster Posey, Zack Minasian, and a pitching coach to be named later is to figure out Birdsong’s role and then lock him into that until he pitches himself out of it. The Giants have a glut of mis-developed prospects or prospects that haven’t panned out, but it’s too easy to say that Birdsong is one of those. I think the path of least resistance is simply sticking him in the bullpen. The Giants are going to need some talented arms there. Despite a poor 2025, Birdsong’s raw talent still rates as undeniable.
