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Scouting Report
Updated May 19, 2026
Riley O'Brien is a 31-year-old relief pitcher for the St. Louis Cardinals who has emerged as an unlikely bullpen breakout success story in 2026. Originally drafted by Tampa Bay in 2017 and traded through multiple organizations, O'Brien joined the Cardinals in November 2023. After showing improved strikeout rates and walk rates in 2024, he has become one of the most productive relievers in baseball this season. His elite stuff features a 98.3 mph sinker with above-average movement and a sweeper with unique characteristics. O'Brien has stabilized the Cardinals' bullpen and is being considered as a potential closer option for the team.
Strengths
- + Late-blooming pitcher with elite strikeout rate
- + Significantly improved K%-BB% ratio
- + Exceptional sinker velocity (98.3 mph) with above-average drop and ride
- + Effective sweeper with unique movement characteristics
- + One of the most productive relievers in baseball through May 2026
- + Stabilizing force for Cardinals bullpen
- + Statcast metrics show elite performance (sea of red)
- + Improved Chase%, Whiff%, K%, and BB% metrics
- + Potential closer candidate for 2026 season
Weaknesses
- - Late career bloomer (age 31) with limited MLB track record
- - Struggled with K%-BB% ratio early in minor league career
- - Mixed early results in 2024 despite strong FIP
- - Small sample size for current elite performance
- - History of injuries that have sidelined him
About
Riley Mahan is a second baseman for the Milwaukee Brewers.
Player Overview
2B
Milwaukee Brewers