Joe Kelly has been a solid pitcher for the Cardinals since arriving in the majors in 2012. He's bounced between the bullpen and the rotation, but has spent most of his time in the latter role, accumulating 213 of his 266 career innings as a starter. Now he's with Boston after coming back as part of the return in a trade for John Lackey, and finds himself in a much different situation. Besides Clay Buchholz, he has the most experience of any Red Sox starting pitcher currently slated for the 2015 roster.
That doesn't mean he'll be the second-best starter on the team: if he is, the Red Sox will be looking forward to 2016 in a hurry. Kelly might be the source of something the Red Sox have none of at the moment after dealing both Jon Lester and John Lackey, however, and that's stability. Buchholz has been all over the place, either pitching dominantly or horribly, and the rest of the rotation -- as of right now -- is set to be filled out by prospects and present-day rookies.
Kelly won't miss a lot of bats as a starter, as he's struck out just 5.5 per nine in his 38 career starts, but he also has induced over 50 percent ground balls in each of his three seasons in the majors. He could be a fit at the back-end of the Sox' rotation, helping give Boston solid innings while limiting the number of rookies or kids who will be pitching in the rotation at any one time. Kelly is plenty young himself, too: he's just 26 this year, and isn't set to be a free agent until 2019. He won't even be arbitration-eligible until 2016.
If nothing else, Kelly will be a useful piece to stash in the bullpen should the Red Sox have better than expected luck with Brandon Workman, Rubby De La Rosa, Anthony Ranaudo, Allen Webster, Henry Owens, and Brian Johnson. He could serve much the same role he did in St. Louis, as a pitcher capable of starting who pitches wherever he's most needed. If too many of the kids need to go to the pen or back to the minors, let Kelly keep starting. If Owens forces his way into the big-league scene at a time when Workman, Ranaudo, or whomever has proven themselves rotation-worthy, then put Kelly back in the pen.
He's not the kind of arm who is going to save a rotation, especially not one with as many question marks as Boston's. If the Sox can acquire a quality arm, though -- one that's well above-average -- for 2015, and they have Buchholz, Kelly, and a couple of kids, then things aren't bleak. There are still questions to be answered -- how good will those kids be, which version of Buchholz will show up -- but Kelly gives them one fewer thing to worry about.