While the St. Louis Cardinals' bullpen hasn't been great overall this season, the club does have one of the most intriguing relievers in the league right now in Riley O'Brien. O'Brien is 31 years old and is under team control through the 2030 season. O'Brien has appeared in 15 games so far this season for St. Louis and has a 1.17 ERA and eight saves across 15 1/3 innings pitched. His advanced metrics are even better. Right now, he's in the 97th percentile in expected ERA, 96th percentile in fastball velocity, 100th percentile in walk rate, 98th percentile in ground ball rate, and 88th percentile in expected batting average against him. Right now, the Cardinals are one of the best stories in baseball. St. Louis is 19-13 on the season and looks more like a playoff team, than a team that is going to blow things up around the trade deadline. But we've also got to remember that the goal of this season is development for the young roster. That's why as the Cardinals traded veterans away this past offseason, St.…