After high school,Woo enrolled at Cal Poly to play college baseball for the Mustangs. Cal Poly was the only school that recruited him as a pitcher rather than a two-way player. As a freshman in 2019,he pitched to an 9.13 ERA over 23+2⁄3 innings.[9] He returned to play for the Oilers that summer and was named the league's top pro prospect.[10][11] He pitched only 17+2⁄3 innings as a reliever for Caly Poly in 2020 before the season was cancelled due to the COVID-19 pandemic. In 2021, he had a 6.11 ERA over 28 innings before undergoing Tommy John surgery and missing the rest of the season.[12] Woo started six of the 31 games he pitched in college, finishing with a 4–7 win–loss record, one save, a 6.49 ERA, and 89 strikeouts in 69+1⁄3 innings.[13][9]
Professional career
The Seattle Mariners selected Woo in the sixth round with the 174th overall selection of the 2021 Major League Baseball draft.[14][15] He signed with the Mariners for $318,200, $31,700 above the slot value of the draft pick.[16][17][18] Still recovering from elbow surgery, he made his professional debut in June 2022 with the Arizona Complex League Mariners. In one game, he was rushed to the hospital after being hit in the face by a line drive but was not seriously injured.[2] He was promoted to the Low-AModesto Nuts later that month, then the High-AEverett AquaSox at the end of July.[19][20] Over 16 starts for the three clubs, Woo posted a 1–4 record with a 4.11 ERA and 84 strikeouts in 57 innings.[21] He played in the Arizona Fall League for the Peoria Javelinas after the season.[19] Coming back from his injury, Woo prioritized throwing his fastball.[22]
Woo started 2023 with the Double-AArkansas Travelers.[23] In nine starts, he had a 3–2 record and 2.05 ERA with 59 strikeouts in 44 innings pitched.[21] He began throwing a sinker in Double-A.[22] On June 2, the Mariners announced that Woo would be promoted to the major leagues to start the following day against the Texas Rangers.[24] Starting in place of Marco Gonzales, Woo had had a rough debut, allowing six runs in two innings.[25][26][27] He won his first MLB game in his fourth start, besting the New York Yankees on June 22. He finished his rookie season with a 4–5 record, 4.21 ERA, and 92 strikeouts in 87+2⁄3 innings.[28]
Despite several injuries, Woo improved in 2024. He began the season on the injured list with elbow inflammation.[29][30] He made his first start on May 10. In his first six starts, he posted a 1.07 ERA, the lowest in Mariners history to begin a season.[31][32][5] He was scratched from his next start on June 11[33] and made two more starts, earning losses in both outings, before returning to the injured list on June 25 with a hamstring injury. He was activated on July 12, resuming his turn in the Mariners rotation.[31][34][35] He ended 2024 with a 9–3 record and 2.89 ERA, striking out 101 batters in 121+1⁄3 innings over 21 starts, all improvements from his rookie season.[36] He was the best MLB starting pitcher at avoiding base on balls, walking 2.6 percent of batters faced.[37]
Woo was the Mariners' most consistent pitcher in 2025.[38] He was named to the All-Star Game.[39] On July 10, he brought a no-hitter into the 8th inning against the Yankees.[40] Before the All-Star break, he ranked third in the American League in strikeout-to-walk ratio and walk rate and accumulated more strikeouts than in either of his two previous seasons.[41] Woo pitched at least 6 innings in his first 25 starts, a franchise record.[42][43] During that stretch, he also allowed no more than two walks, the longest stretch to start a season since Cy Young in 1905.[44][45] That consistent length benefitted the Mariners' bullpen.[46] Woo struck out a career-high 13 batters on September 13 in a win over the Los Angeles Angels.[47]
Pitching style
Woo primarily throws a four-seam fastball and sinker that both average 95 miles per hour (153km/h). His offspeed pitches are a changeup and slider (some of which are labeled a sweeper).[48][49] He throws his fastball and sinker close to 75 percent of the time, more frequently than most of his contemporary starters. He also throws a high percentage of strikes, which limits his base on balls.[50][32][51][22] Woo throws from a low arm slot and has a low release point and smooth delivery, which can make it difficult for batters to hit his pitches hard.[12][52][53][54][22]
Personal life
Woo was born in Oakland, California and grew up in the San Francisco Bay Area with his parents and sister.[9][55] His parents attend all his MLB starts.[update][56] His paternal grandparents were born in China and moved to the United States.[57][58] He visited China twice as a child.[59] His maternal grandfather died in July 2025, during Woo's final start before he pitched in the All-Star Game.[56]
As a child, Woo was a fan of the San Francisco Giants. His favorite player was Brandon Crawford.[5][60] In 2024, Woo became the last person born in Oakland to play an MLB game in Oakland.[61]
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