The San Diego Padres signed two relievers this off-season to bolster its bullpen, bringing in Yuki Matsui and Woo-suk Go. Matsui comes to MLB as an international free agent after 10 seasons with NPB’s Rakuten Eagles, while the more recent signing of Go came as a surprise after Go was posted by KBO’s LG Twins. Both will be pieces in a revamped Padres bullpen.
Yuki Matsui
| Season | IP | ERA | Saves/Save Opp. | Strikeouts | Walks | K-BB% |
| 2022 | 51 2/3 | 1.92 | 32/34 | 83 | 19 | 33% |
| 2023 | 57 1/3 | 1.57 | 39/42 | 72 | 13 | 26% |
What does he do well?
Standing at 5’8”, Matsui is on the smaller side for MLB pitchers (he’d have been the 3rd-shortest pitcher in the majors last season) but uses his small stature to create some good pitch-shape characteristics. His fastball creates some carry from a lower release point due to his height, especially through the top of the zone.
His splitter is a nasty platoon-neutral pitch that disappears at the bottom of the zone, with an insane 56% whiff rate in 2023. He used the pitch more down and away from RHHs, but he can also throw it below the zone to left-handed batters with good results.
Mechanics
Matsui also has a glove tap as he gathers himself at the top of his delivery. Creating a weight shift back as he lifts his leg, there’s a little pause as he balances. With a tiny pat of the ball in his glove he then comes forward and extends his leg out as his hip leads.
One quirk is that Matsui darts his eyes up to the sky as he comes into foot strike, and the eyes don’t fixate back on the target until after the ball is released.
The Arsenal
| Pitch Type | Usage | Velocity | Strike % | Whiff % |
| Fastball | 52% | 92.5 mph | 66% | 23% |
| Splitter | 35% | 87.5 mph | 64% | 56% |
| Slider | 11% | 86 mph | 69% | 35% |
| Curve | 2% | 76 mph | 74% | N/A |
Matsui’s go-to pitches are his fastball and splitter. He works the fastball up and away from right-handed batters, tunneling his splitter out of that same spot the majority of the time, throwing the two pitches on the outer part of the plate.
Against left-handed batters, his splitter works more middle of the zone down and he still tries to spot his fastball away from lefties on the glove side. One weapon for Matsui, especially against lefties, is Matsui’s slider. With good movement, he’s able to pound the bottom of the zone glove side. He would usually break out the slider and curve against the better left-handed hitters in Japan.
Here’s a slider and fastball against Kensuke Kondoh, the best pure hitter in Japan:
The video below is a splitter and curveball followed by a slider. I cut out some pitches in the at-bat for the sake of time, but this seven-pitch at-bat against Yuki Yanagita displayed Matsui’s full arsenal.
The pitch becomes an offering that moves away from lefties, but he is unafraid to bury the pitch down and in toward righties knees. With flashes of above-average command last season, Matsui found a formula that worked for him.
While he has displayed below-average control in some past seasons, he might have turned the corner with a 5.9 BB% in 2023. You don’t become the youngest player in NPB history to 200 saves without having some control and nasty offerings.
What to Expect
Matsui will compete for the closer role in San Diego but also could work well as a setup man or seventh-inning guy to start the season. He has two above-average to plus secondaries that should help against both right and left-handed hitters. He might alter his pitch usage slightly, but his high carry four-seam should prove a weapon even if thrown more 92-93 mph.
Matsui struggled to adjust to using a different ball during the WBC, so his acclimation to the league, like Go, might take some time. Still, if he can keep his walks down like he did in 2023 success as a high-leverage reliever should follow.
Woo-suk Go
| Season | IP | ERA | Saves/Save Opp. | Strikeouts | Walks | K-BB% |
| 2022 | 60 2/3 | 1.48 | 42/44 | 80 | 21 | 24% |
| 2023 | 44 | 3.68 | 15/17 | 59 | 22 | 19% |
After seven seasons with the LG Twins, Go was posted with a more shallow market for his services after an injury-plagued 2023 in which he missed time in May and his ERA ballooned after some bad outings. The most notable clunker came on April 30 when he walked two and gave up a weird high chopper for an RBI single. Then, three pitches later, he threw his slowest fastball of the year on a three-run home run. He was lifted and didn’t pitch again until June 4 due to an injury in his lower back.
He compiled a 31% strikeout rate last season to go with a high 12% walk rate. Go is a power pitcher who aggressively sprays the ball in and out of the zone and is an uncomfortable at-bat when he’s hitting his spots.
What does he do well?
Go is the hardest-throwing reliever in KBO, touching 98 mph on his fastball and comfortably sitting around 95 mph. His fastball gets flat at times, but he still has decently loud stuff for an MLB bullpen.
Go’s arsenal is MLB caliber but with spotty control and command; he must consistently harness his secondary pitches and keep his fastball out of the middle of the zone. At times, he tries to be too fine with his pitches instead of trusting his stuff to play in the zone.
Always felt Woo-suk Go had stuff to become a reliable middle reliever at #MLB. The problem that I’ve seen from over the yrs is that he over-thinks and that has backfired a “few” occasions. Building/maintaining confidence and trusting his stuff is going to be huge for Go! #Padres pic.twitter.com/aFNClk5bx4
— Daniel Kim 대니얼 김 (@DanielKimW) January 4, 2024
There are numerous examples of cycling through pitch types with the catcher and trying to spot pitches perfectly on the edges.
LG combatted by having their catcher set up in the middle of the zone and letting him rip pitches. Middle-of-the-zone fastballs won’t play as well in MLB, but he still throws 95 mph with a decent curve.
Go pitches and feeds off of emotion and confidence so when he’s rolling he becomes even better. Bad outings can get away from him quickly because of walks. His stuff in KBO would just overpower lineups but stateside he needs to limit the walks for success.
Mechanics
Go has tinkered with his windup mechanics in terms of rhythm and timing. At points, he incorporated a glove tap into his movements and then he would completely scrap it during some outings or lessen it. To end 2023, he went back to a more substantial glove tap at the top of his leg lift.
The Arsenal
| Pitch Type | Usage | Velocity | Strike % | Whiff % |
| Fastball | 57% | 94.5 mph | 60% | 25% |
| Cutter | 24% | 91 mph | 64% | 28% |
| Curve | 15% | 83 mph | 65% | 49% |
| Slider | 3% | 85 mph | 50% | 46% |
Go tunnels his arsenal best when he works the zone vertically. Peppering the top of the zone with fastballs and then snapping off sharp breakers below the zone for chase. His curve has a baby spike grip and he can work the pitch both in and out of the zone.
Curveball Grip
He gets some gnarly chase swings at pitches and uses his curve to both righties and lefties. Against lefties, he will backdoor curves deeper into counts as well.
Go primarily uses his cutter to keep hitters off his fastball. He is comfortable throwing the pitch glove so that it’s in on the hands of lefites or down and away to righties. He occasionally throws it arm side on the edge versus left-handed batters.
He also has a slider that he will use against better hitters. His cutter and slider have very similar grips.
Slider
Cutter
With the cutter, Go stays behind the ball, and on the slider, he tries to get to the outside of the ball. There are subtle differences in movement and velocity but based on signs he has thrown both pitches.
In San Diego, the team might try to tweak his slider and play around with grips to get even more horizontal movement, and with pitchers like Darvish on the team who helped Rōki Sasaki with his slider, Go might find a tunnel horizontally that works for him.
With his sporadic control, a more consistent slider could help Go pitch not only north and south but also east and west so he doesn’t have to be as fine and can still generate whiffs.
What to Expect
Go projects as a middle relief option who has experience at the back of a bullpen and if he can gain confidence and trust his stuff, could see his role expand during the season. With his fastball and curveball, he should have no issues facing both lefties and righties out of the pen.
