Ryan Dempster, Quality AL Pitcher

According to Ken Rosenthal, Ryan Dempster is close to signing with the Boston Red Sox. Assuming the deal gets done, you’re going to hear a lot about how Dempster is an NL pitcher transitioning to the AL East, and how this is bound to go poorly. You’re going to hear about Dempster’s 5.09 ERA with Texas after the mid-season trade ended his long stint as an NL only pitcher, and you’re going to hear about how he got taken apart by the Yankees, giving up eight runs in six innings of work.

Because Dempster is headed for his age-36 season, has a fastball that sits around 90 mph, and had spent his entire career in the NL before the mid-season trade to Texas, many are going to expect Dempster to be exposed in the AL East. Whenever a pitcher without top-shelf velocity makes the move from the NL to the AL, and especially to the AL East, there’s always an expectation of disaster. The theory goes that pitchers with marginal velocity can dominate in the NL, but get exposed when facing the big bats of the super scary American League East.

The problem is that we’ve got too many pieces of evidence to suggest that it’s not true.

Last year, the guy making the big move was Hiroki Kuroda. At 37, he was leaving Dodger Stadium and the NL West for the Yankees, and he was going to find out just how different life was on the east coast, with the warm summers, small ballparks, and fearsome offensive line-ups. Instead of regressing, Kuroda had perhaps the best season of his career. His ERA- of 79 was tied for the sixth best mark in the league, and his peripheral numbers all head steady, even his strikeout rate. There was next to no difference between NL West Kuroda and AL East Kuroda.

Kuroda wasn’t the only NL West pitcher who made his way to the AL East last year. Jason Hammel was traded from Colorado to Baltimore in exchange for Jeremy Guthrie, and while leaving Colorado is always good for a pitcher’s career, landing in Baltimore didn’t seem like a huge improvement for a guy who had already been bounced out of the division after struggling in his early career with the Devil Rays. Instead, Hammel reinvented himself, added a two-seam fastball and some velocity, and posted career bests in bsaically every relevant pitching category. Hammel’s career HR/9 before last year was 1.06, but then he took his act to Baltimore and allowed 0.69 HR/9 while transitioning back to the AL East.

Going back to 2011, we see soft-tossing right-handers Carlos Villanueva and Freddy Garcia coming east, with Villanueva also making the switch from the National League. Over the last two years, Villanueva has posted an ERA- of 100, while Garcia has come in at 102, both improving over their performances with their previous clubs. And neither are exactly what you’d call stuff guys.

Even international rookies Miguel Gonzalez and Wei-Yin Chen had few problems transitioning to the AL East last year, despite throwing fastballs that sit around 91 and lacking anything resembling a true out pitch. Chen and Gonzalez both posted ERAs that were significantly better than their secondary results would suggest, but even with expected regression, they performed better than expected given their stuff and the supposed heightened level of competition in that division.

Yes, the AL East features some good offensive clubs, some smaller ballparks, and the heat and humidity of on the eastern seaboard allows the ball to carry better in the summer months than it does out west. Yes, the DH means that fringy pitchers have to get an extra big league hitter out each time, and can’t pitch around the bottom of the order the same way they can in the NL. Pitching in the AL East is harder than pitching in the NL Central.

But, the difference isn’t so large that it should be expected to turn a good pitcher into a bad one, and make no mistake, Ryan Dempster is a good pitcher. He’s posted an xFIP- between 85 and 96 every year since 2005, so while variation in BABIP and LOB% has caused his results to jump around a bit, he’s always regressed right back into being an above average hurler. Last year, his ERA was artificially low in Chicago because of a .255 BABIP, and it was artificially high in Texas because of a .330 BABIP. He didn’t magically get worse when he moved to the AL – his BABIP was just bouncing around randomly, as BABIPs do from time to time. In fact, he actually increased his K% after moving to the AL, which doesn’t really fit into the “NL pitcher” narrative.

Headed into his age-36 season, Dempster is almost certainly on the downside of his career, and can be expected to get a little worse just from natural aging. It’s probably safter to project him as an average pitcher for the next few years rather than an above average one. But, there’s really no reason to think that he’s just going to find the AL East so inhospitable that he’s incapable of getting hitters out, or that there’s any real evidence that pitchers without big time stuff fall apart once they have to face the Yankees a few times each year. Adjusting for quality of competition and the differences between leagues is one thing; pretending that there’s a gap so large that pitchers can’t successfully move from the NL to AL East is just not representative of reality, however.