He isn't exactly the household name that Jung Hoo Lee is. Not yet. But if you’ve spent any time refreshing the San Francisco Giants’ transaction wire over the last two years, you know the name Kai-Wei Teng. Honestly, his journey has been a bit of a roller coaster, the kind that makes fantasy managers pull their hair out and scouts squint at their radar guns.
The raw Kai-Wei Teng stats from the 2025 season don't tell the whole story. On paper, a 6.37 ERA across 29.2 big-league innings looks rough. Kinda ugly, actually. But if you dig into how those innings happened—and why the Giants kept going back to him—you see a pitcher who is starting to figure out how to survive in the most unforgiving environment in sports.
👉 See also: Who's Pitching for the Giants Today: The Rotation Reality vs. Offseason Hype
The 2025 Campaign: By the Numbers
Last season was basically a tale of two pitchers. After a brutal 2024 cup of coffee where he posted an ERA nearly touching double digits (9.82, to be exact), Teng went back to Triple-A Sacramento and absolutely shoved. He posted a 3.67 ERA in the Pacific Coast League, which, if you follow the PCL, is basically like pitching on the surface of the sun. He was striking out nearly 14 batters per nine innings.
When the Giants called him back up in August 2025, things looked different. He wasn't just a "fill-in" guy anymore. He was actually missing bats.
- Strikeout Rate (K%): 28.1%. That's legitimate. For context, the MLB average usually hovers around 22-23%.
- Walk Rate (BB%): 12.2%. This is the problem. You can't walk that many guys and expect to keep your ERA under four.
- The Velocity: His four-seam fastball averaged about 93.1 mph. It’s not "blow-you-away" heat, but it’s enough to set up his real weapons.
His first MLB win finally came on August 8, 2025, against the Nationals. He didn't even start that game; he came in after Matt Gage and tossed five solid innings. It was a moment of pure relief for a guy who had been designated for assignment (DFA’d) just months prior.
Why the Slider is Everything
If you look at his pitch mix, it’s pretty weird. Most guys throw their fastball 50-60% of the time. Teng? He throws his slider almost 40% of the time. It’s his security blanket.
The Statcast data from 2025 shows that his slider has some serious horizontal "sweep." When he’s on, he’s tunneling that slider off his sinker, making hitters look silly. When he’s off, he’s nibbling at the corners and falling behind 2-0 or 3-1. That’s where the high walk rate comes from. He’s sorta afraid to give in with the heater because, frankly, MLB hitters eat 93 mph for breakfast if it’s over the heart of the plate.
The "Innings Eater" Myth
People kept calling him a potential back-of-the-rotation starter. I'm not so sure. In 2025, the Giants used him in 8 games, but only 7 were starts. His longest outing was just five innings. To be a real MLB starter, he has to prove he can get through a lineup a third time. Right now, his Kai-Wei Teng stats suggest he’s much more effective as a "bulk" reliever—the guy who comes in after an opener and gives you 12 outs.
Breaking Down the 2024 vs. 2025 Jump
The improvement was real. Even if the ERA doesn't scream "Ace," look at the peripherals.
| Metric | 2024 Season | 2025 Season |
|---|---|---|
| Innings Pitched | 11.0 | 29.2 |
| WHIP | 2.09 | 1.55 |
| Batting Avg Against | .326 | .254 |
| Hard-Hit % | High | 31.6% |
A .254 opponent batting average is a massive step up from the .326 he allowed in 2024. He’s becoming harder to hit. Now he just needs to stop hitting people—he plunked seven batters in 2025. That’s a lot for 29 innings.
What Most People Get Wrong About Him
There’s this narrative that he’s just a "soft-tosser." I’ve heard it on plenty of Giants broadcasts. But his Max Velocity in 2025 actually touched 95.6 mph. The arm strength is there. The issue is "spin efficiency." The Giants' pitching lab has been working with him to make his fastball look like it’s rising rather than sinking. If he can get that four-seamer to stay up in the zone, his curveball—which has a massive 8.0-inch drop—becomes a nightmare for lefties.
He’s currently 27. In pitcher years, that’s "now or never" territory. He’s pre-arbitration eligible for 2026, meaning he’s a cheap, high-upside arm for a Giants team that is always looking for value.
The 2026 Outlook
So, what’s next?
The projections for 2026 are actually kinda optimistic. FanGraphs (via DC) has him pegged for about 33 innings with a significantly lower ERA of 4.13. That would be a huge win. If he can cut the walks down from 12% to maybe 9%, he stays on the roster all year.
He recently made the decision to skip the 2026 World Baseball Classic. Honestly, that was a smart move. He needs a full Spring Training in Scottsdale to secure his spot. Representing Taiwan is a huge honor, and he’s done it before (the 2023 WBC and the 2019 Asian Baseball Championship), but his MLB career is at a tipping point.
Actionable Insights for Fans and Managers
If you're tracking Kai-Wei Teng or looking at his stats for a fantasy deep league, keep an eye on these three things:
- The BB/9 Rate: If he’s walking more than 4 guys per nine innings in April, he’s going back to Sacramento. If it’s under 3.5, he’s a keeper.
- The Sweeper Usage: Watch if he starts throwing the sinker more to righties. He needs a pitch to get early contact so he doesn't have to rely on the "strikeout or walk" outcome every time.
- The Opener Strategy: The Giants love using him behind an opener. His stats are much better when he starts the 2nd inning rather than the 1st.
He’s a unique piece of the Giants' puzzle. He’s got the build of a workhorse—6’4”, 260 lbs—but the finesse of a mid-rotation specialist. Whether he becomes a permanent fixture in the San Francisco rotation or a high-leverage long-man depends entirely on whether he can master the strike zone in 2026. The stuff is major-league quality. The command? Still a work in progress.