Riley O'Brien

Riley Chun-Young O'Brien (born February 6, 1995) is an American professional baseball pitcher for the St. Louis Cardinals of Major League Baseball (MLB). He has previously played in MLB for the Cincinnati Reds and Seattle Mariners. He made his MLB debut in 2021.

Amateur career
O'Brien attended Shorewood High School in Shoreline, Washington, where he played baseball. He graduated in 2013, and then enrolled at Everett Community College. After two seasons at Everett, he transferred to the College of Idaho. As a junior in 2016, he went 6–3 with a 3.23 ERA and sixty strikeouts over 69 innings. In 2017, his senior year, he pitched to a 3–4 record and a 2.15 ERA over 67 innings. After the season, he was selected by the Tampa Bay Rays in the eighth round of the 2017 Major League Baseball draft.

Tampa Bay Rays
O'Brien signed with the Rays and made his professional debut that year with the Princeton Rays of the Advanced Rookie Appalachian League, going 1–0 with a 2.20 ERA over 11 games (ten starts). During the season, he was named Appalachian League Pitcher of the Week twice. In 2018, he began the season with the Bowling Green Hot Rods of the Single–A Midwest League (with whom he was named an All-Star) before being promoted to the Charlotte Stone Crabs of the High–A Florida State League, with whom he ended the year; over 25 games (13 starts) between both teams, he went 8–4 with a 2.75 ERA. In 2019, he began the season with Charlotte and was promoted to the Montgomery Biscuits of the Double–A Southern League in May. Over 20 games (17 starts) with the two clubs, he pitched to a 7–6 record and 3.16 ERA.

O'Brien did not play in a game in 2020 due to the cancellation of the minor league season because of the COVID-19 pandemic.

Cincinnati Reds
On August 28, 2020, the Rays traded O'Brien to the Cincinnati Reds in exchange for Cody Reed. On November 20, 2020, the Reds added O'Brien to their 40-man roster to protect him from the Rule 5 draft. To begin the 2021 season, he was assigned to the Louisville Bats of the Triple-A East. Over 23 games (22 starts), O'Brien pitched to a 7–7 record, a 4.55 ERA, and 121 strikeouts over $112 2⁄3$ innings.

On September 28, 2021, the Reds recalled O'Brien to the active roster to make his MLB debut versus the Chicago White Sox. He was the starting pitcher and threw $1 1⁄3$ innings, giving up two solo home runs while walking three and striking out two.

On April 13, 2022, the Reds designated O'Brien for assignment to make room for Nick Lodolo.

Seattle Mariners
On April 16, 2022, the Reds traded O’Brien to the Seattle Mariners for cash considerations or a player to be named later. (On June 3, minor league infielder Luis Chevalier was sent to Cincinnati to complete the trade). He was designated for assignment on May 27. He cleared waivers and was sent outright to the Triple-A Tacoma Rainiers on June 2.

O'Brien spent the entirety of the 2023 season in Triple–A with Tacoma. In 51 appearances, he registered a 2.29 ERA with 86 strikeouts and 15 saves across 55.0 innings of work.

St. Louis Cardinals
On November 5, 2023, O'Brien was traded to the St. Louis Cardinals and subsequently added to the 40–man roster. On March 26, 2024, the Cardinals officially revealed that O'Brien had made the Opening Day roster. On March 31, he was placed on the injured list with a flexor strain, and was transferred to the 60-day injured list on May 6.

Personal life
Riley is married to Chellyn O'Brien, they had their wedding in late 2023. O'Brien's grandfather, Johnny O'Brien, played six seasons in the major leagues. His great uncle Eddie O'Brien also played in the majors.