When the then-Oakland Athletics acquired Adam Oller before the 2022 season, they were sufficiently interested in the then-27-year-old to put him straight onto their Opening Day roster. Truth be told, they were also sufficiently short of established arms enough to give some newcomers a try. By the end of the following year, though, after Oller had produced some of the worst pitching numbers in the major leagues, he had already been cut.
Three years later, Oller has found considerably more success on the other side of the world.
Now in his second season with the KIA Tigers of the KBO League, Oller has emerged as one of South Korea’s better starting pitchers. Through 23 starts in 2026, the big right-hander has an 11-9 record with a 3.01 ERA, 1.06 WHIP and 144 strikeouts in 134.2 innings. Opponents are batting only .204 against him, and he has recorded 15 quality starts, including one complete-game shutout.
Among KBO pitchers to have worked at least 100 innings this season, Oller ranks fifth in ERA. His WHIP is also one of the best in the league, while his 99 hits allowed mean he is surrendering only 6.6 per nine innings. It is a long way removed from his time in the Athletics’ organization.
Oller’s Athletics Career
Oller had taken an unusual route to the majors in the first place. A 20th-round draft pick by the Pittsburgh Pirates in the 2016 Major League Baseball Draft, he was released two years later, and subsequently pitched in independent baseball before earning another opportunity with the San Francisco Giants. He later joined the New York Mets via the minor league phase of the Rule 5 Draft, and enjoyed a breakthrough minor-league season in 2021, pitching across Double-A and Triple-A and putting himself on the verge of the majors. However, it had taken until the age of 27 to get beyond the A-ball level – the window was already very small.
Despite being added to their 40-man roster, Oller never appeared for the Mets, and instead was traded to the Athletics alongside fellow pitching prospect J.T. Ginn in March 2022 in the deal that sent Chris Bassitt to New York. He made his MLB debut less than a month later and went on to appear 19 times for the Athletics during his rookie season, including 14 starts. The results, however, were poor. He went 2-8 with a 6.30 ERA and 1.63 WHIP across 74.1 innings, allowing 82 hits and 17 home runs while walking 39 and striking out only 46. Opposing hitters produced a .916 OPS against him. He made everyone into Junior Caminero.
The Athletics brought him back in 2023, but there was little improvement. Oller made nine appearances, predominantly in relief, and surrendered 24 runs in only 19.2 innings. Opponents batted .341 against him with a .992 OPS, while he walked 12 and struck out 13, with his ERA for the season finishing at 10.07. Second time around, he made everyone into Yordan Alvarez.
The Athletics placed Oller on waivers that July, whereupon the Seattle Mariners claimed him. But Oller did not return to the majors that season, instead finishing the year in Triple-A – he had already recorded a 7.11 ERA in 12 appearances for the Athletics’ Las Vegas affiliate before the move, and did not much improve with the Mariners.
Turning It Around On The Other Side Of The World
There was another stint in the majors to come. After spending time in the Cleveland Guardians organization, Oller joined the Miami Marlins in July 2024, and returned to the majors in August. He was better than he had been in Oakland, making eight starts and posting a 5.31 ERA over 42⅓ innings. He struck out 36, but again struggled with walks, issuing 22, taking Oller’s career major-league totals to a 5-13 record and 6.54 ERA across 36 appearances, with 43 home runs, 76 walks and 136.1 innings. It was not enough, though, for more major league work.
Rather than continuing to pursue another minor-league opportunity, Oller signed with KIA for the 2025 season. And better results followed immediately. He made 26 starts in his first KBO campaign, going 11-7 with a 3.62 ERA and 1.15 WHIP across 149 innings; most strikingly, the pitcher who had struggled to miss bats in Oakland struck out 169 hitters. He allowed only eight home runs all season, fewer than half the 17 he had surrendered in just 74⅓ innings during his first year with the Athletics.
Oller has improved again in 2026. His ERA has fallen from 3.62 to 3.01 and his opponents’ batting average sits at .204. Earlier this season, he briefly led the entire KBO in ERA and was tied for the league lead in victories, earning a selection to the Nanum roster for the KBO All-Star Game. Across his two KBO seasons, Oller now sports a 22-16 record with a 3.33 ERA, 1.11 WHIP and 313 strikeouts in 283.2 innings.
Despite his slow start as a pro, there was never much doubt that Oller had enough ability to reach the majors. He received looks from multiple organizations at that level for a reason. Staying there was the problem. But Korea has provided a very different outcome. Oller has gone from one of the least effective pitchers on an Athletics team that lost 112 games in 2023 to an All-Star and one of the KBO’s leading starters. As can often be the case for fringe Major Leaguers, South Korea has proved to be quite a revival.
Former Athletics Wash-Out Revives Career in Korea