Aaron Harang isn't anything special at this point. The Dodgers replaced the need for him in their own rotation last year when acquiring Josh Beckett from the Red Sox, then piled on to that this off-season by signing Zack Greinke. It's not that Harang is their equivalent, it's just that he was meant to occupy one of the rotation spots that both of those arms took, and things were crowded out in Los Angeles even before they came on board. So, the Dodgers sent him to Colorado, and the Rockies designated him almost immediately upon acquiring him. This series of events ended Thursday with a trade to the Mariners for a fringe minor-league reliever.
However, don't let this fool you into thinking there's nothing he can do to contribute. He was a wreck in 2010, one that was dealing with arm injuries that had helped knock him from his three-year peak to begin with, and that's how people kind of forgot he existed as a useful entity to begin with. In 2011 and 2012, however, out of the offense-heavy Great American Ballpark, Harang posted a 101 ERA+ over 350 innings split between the Padres and Dodgers. Yes, he won't have the luxury of either Petco Park or Dodger Stadium and their pitcher-friendly tendencies anymore, but now that he's in Seattle with the Mariners, he does have an American League version of those environments at his back.
The Mariners were using Blake Beavan as their fifth starter, and there is a good chance he'll be pushed to the bullpen in favor of Harang. Given Beavan's career ERA+ in 260 innings and 43 career starts is just 84, and that he's had a serious home run problem despite his pitcher-friendly home park, he's the easy choice, and a clear spot for Harang to upgrade on. There is a much better chance, even in 2013, for Harang to be productive than for Beavan, who was never a top prospect or anything like that, to suddenly figure it out as a starter.
There is, of course, the question of how a pitcher coming from the NL to the AL will do. It's a legitimate concern, too, especially for someone like Harang who has had it easy in the NL West the last two years. Plus, Harang has crushed the opposing pitcher when they come up to bat, limiting them to a 282 OPS in 2011 when the NL as a whole was at 482, and holding them to 363 last season while the NL stood at 465. Designated hitters, even bad ones, are going to do much better than that, and Harang's production will suffer for it.
That being said, Beavan was all kinds of not productive, and so the bar Harang has to clear in order to be an upgrade is probably somewhere around his floor as a starter at this point. He can be a bit below-average and still have the Mariners coming out ahead.
What's a little odd about this whole thing is that the Mariners cut Jon Garland this spring. Garland, like Harang, is a guy who can be average for enough innings to make it worth a team's time, and he even has the benefit of being left-handed. Garland went and signed with the Rockies -- it's part of the reason there wasn't any room for Harang there -- and while we might get a better sense of why the Mariners cut him with more time, right now, after quickly changing their minds about their available options, it's something to ponder.