In the aftermath of the Indians' blockbuster acquisition of Yankees reliever Andrew Miller, the St. Louis Cardinals made a move for a less acclaimed bullpen arm who will nonetheless be expected to contribute right away to the Major League club: White Sox lefty Zach Duke.
Duke, whom you may remember from his time as a starting pitcher for the Pittsburgh Pirates, reinvented himself as a left-handed bullpen option in his 30s. The 33 year-old has 53 appearances in 2016, amassing 37 2/3 innings while generating a 2.63 ERA, a 3.03 FIP, and a 3.26 xFIP. While Duke is a lefty, and the Cardinals have not had a true LOOGY specialist this season, his splits in 2016 have been relatively moderate, though for his career, left-handed hitters do have a 36 point lower wOBA than righties.
The price for Duke, however, does not appear to be inconsequential. Charlie Tilson, who began the season as MLB.com's #12 Cardinals prospect, has a 100 wRC+ with AAA Memphis this season, though he has impressed scouts and fans moreso with his speed (he stole 46 bases in 134 games last year at AA Springfield) and his glove.
In the end, the cost for Zach Duke seems about right given the current seller's market landscape. He did not cost multiple top-100 prospects plus two more players like Andrew Miller, but he is also not nearly as good as Andrew Miller. Duke should be an incremental move to make the Cardinals a little bit better. The best recent comparison of this trade for the Cardinals was the 2012 trade which sent Zack Cox to the Miami Marlins for Edward Mujica: in both cases, a regarded prospect was dealt for a good-not-great reliever with an additional year of club control (Duke is signed for 2017 for $5.5 million), and as that turned out, Cox never panned out, and so the deal was fine. And it is far too early to tell with Charlie Tilson.