Seunghwan Oh played in the KBO for Samsung Lions for nine seasons. He then moved to the Japan Central League to play for the Hanshin Tigers for two seasons. After his eleven years in foreign leagues, the St. Louis Cardinals liked enough of what they saw that they extended him a one-year, $2.5 million contract with a club option for the second year that would keep him in St. Louis through the 2017 season.
During his time in both the KBO and JCL, Oh was primarily a closer. He averaged well over ten strikeouts per nine innings in those leagues, and he recorded a total of 357 saves in eleven seasons. Oh rarely pitched fewer than sixty innings in relief each season, and his ERA was below 2.00 in eight of his eleven seasons. He faced a suspension for gambling in 2010, limiting him to only fourteen innings that year.
When the Cardinals signed him, he was entering his age-thirty-three season. While he was a bit older than most free agents, he had plenty of great experience at the back of the bullpen. Oh's role was to be a setup man for Trevor Rosenthal at the time and to give rest to both Kevin Siegrist and Seth Maness.
Oh's first season in St. Louis was very strong. He pitched 79.2 innings (classic Matheny) with 19 saves, a 1.92 ERA, and 11.6 strikeouts per nine innings. Oh was exactly what the Cardinals needed out of the bullpen in 2016. His second season wasn't as strong; his ERA regressed to 4.10 in 59.1 innings. Perhaps Oh was worn out after pitching so many innings the season before, but his sophomore season in the majors wasn't as successful as his first. He went on to play for the Toronto Blue Jays.