Ryan Dempster has been a pretty good pitcher for a pretty solid chunk of his career. He's bounced between starting and relief a bit over the years, but, since 2008, he's been a starter only. The result? Just under 1,000 innings in five seasons, an ERA 14 percent better than the average, and an average of 32 starts per season. That's exactly the kind of production that's been missing from the middle portions of the Red Sox' rotation in the last few years.
Here's the one thing that has people a bit worried about him going forward, however: except for 69 innings in 2012, every frame of Dempster's big-league career has come in the National League. It's been the less difficult of the two leagues for much, if not nearly all, of his career, and that's especially true for pitchers since they get to face their opposing mounds men rather than a designated hitter.
What has kept that worry alive is that, in Dempster's short time in the Junior Circuit, he posted a 5.07 ERA. It's understandable that there would be some concern over this, but it's very likely overblown as well.
Not to make a small sample even smaller, but breaking down Dempster's short stint with the Rangers brings some clarity to what he actually did -- remember, ERA isn't exactly a reliable indicator over a full season of innings, never mind one-third of one. In two of Dempster's first three starts with the Rangers, he allowed eight runs, making that 16 runs in 10-2/3 innings. There is no denying he was hammered in those contests: he gave up four homers between the two, as well as 18 hits. However, these (and one other start) are the only black marks on his Texas record.
In between those two appearances, Dempster tossed 6-2/3 frames against the Red Sox, giving up three unearned runs thanks to an error and a homer. He struck out six batters and allowed just one walk, though, while limiting the Sox to a pretty standard six hits. Not great, but it was a quality start even if you charge the runs to Dempster, and there's nothing wrong with that from a mid-rotation guy on an off day.
Following the last disaster start, Dempster rattled off 49 innings where he gave up a much more normal five homers, struck out 51 batters against 18 free passes, and posted a 3.33 ERA. In August and September when the summer air inflates offense, with four of those starts coming in the Ballpark at Arlington, that's more than an acceptable run. His final start of the year wasn't so good, as it came against the buzz saw that was the Oakland Athletics on their way to stealing away the division from the Rangers. However, even with that, his ERA with the Rangers minus the two horrific starts cited above came out to 3.55.
Even if you don't discount those two appearances, you're still talking about a guy who struck out over a batter per inning, with a 2.8 strikeout-to-walk ratio. Yes, homers were an issue, but that'll happen when you pitch in Arlington in the last months of summer, where he gave up five homers in five games and featured a .361 batting average on balls in play.
Dempster is right-handed, and in his career has been, unsurprisingly, more susceptible to lefty hitters than righties. The Ballpark in Arlington enhances power numbers for hitters from both sides, and while Fenway does that with doubles for left-handers, according to Stat Corner, over the last three years it has reduced homers from the left side by 20 percent compared to your average park. Dempster should see a reduction in his homers, which should more than compensate for any doubles-related trouble Fenway gives him, and he misses enough bats to further balance this potential issue out.
Yankee Stadium might not be the greatest place for him, but it's just one park. The Rogers Centre is neutral for left-handed homers, Tropicana is just about as rude to left-handed home run hitters as Fenway, and the stadiums of the Angels, Athletics, and Tigers all reduce left-handed power output, with the first two doing so as severely and more severely than Fenway, respectively. The only other AL issue besides Yankee Stadium, in terms of teams Boston will face often and in potentially important contests, is that of the Orioles. Hopefully, Dempster is able to avoid those two locales to a degree, but even if he can't, facing lefties hasn't exactly ruined his career to this point, either.
Yes, there's some concern about Dempster's transition to the AL, but looking a little deeper than just his small-sample ERA with the Rangers tells you that there are also plenty of reasons to be optimistic about his two-year deal with the Red Sox. Boston needs him to help anchor the middle of the rotation, fulfilling a goal they've been unable to accomplish since 2010 when John Lackey held it down with innings and an average ERA. That's all Boston needs, and Dempster is certainly capable of as much.