Jeremy Guthrie was the Orioles' most consistent pitcher during his first two seasons at the club. After posting a solid 3.63 ERA in 30 starts during the 2008 season, he cemented himself as the Orioles' ace and, perhaps more important in the long term, one of our best trade chips.
Guthrie is primarily a control pitcher, giving up fewer than 3 walks per nine innings. While he possesses a 93 mph fastball, he doesn't have great stuff, striking out only 6 batters per nine. As with all pitch to contact guys, it was essential that he keep the ball on the ground on a regular basis.
During his first two seasons, he was an adequate groundball pitcher, maintaining a GB/FB ratio of around 1.15. That placed him solidly in the middle of the pack, and was reflected in his HR rate of around 1.15 per 9 innings, which was also close to the league average.
So Guthrie was pretty much the definition of an average pitcher in 2007 and 2008. However, in 2009, he has blown up. As of June 11, he has given up 14 home runs in just twelve starts, leading the American League in that category. He's on pace to give up 42 home runs in a full 200 inning season.
If you look at the rest of Guthrie's peripherals, nothing much has changed. His K/9 has gone up slightly, as has his BB/9. There's no evidence this is anything but random fluctuation, and having watched several of his games on TV, his stuff and control look fine, and his velocity hasn't dropped at all.
The natural conclusion is that his pitches have lost some movement. This is reflected not only in his home run numbers, but in how many flyballs he's given up as a whole. He essentially reversed his GB/FB rates - now, he gives up 1.2 fly balls for every groundball, almost exactly the opposite of his ratio in 2007 and 2008.
Looking at his Pitch Type Values, it becomes apparent that his fastball is the main culprit. In 2008, his fastball was about 13 runs above average for the year, ranking in the top 10 among AL starters. His other pitches were pretty close to average.
So far this year, however, Guthrie's fastball is considerably worse—an awful 10 runs below average. There are only three AL pitchers with a worse fastball—Armando Gallaraga (5.19 ERA in 12 starts), Francisco Liriano (6.12 ERA in 12 starts), and Fausto Carmona (7.42 ERA in 12 starts).
Guthrie and his coaches seem to have realized this. He has thrown fastballs only 57% of the time, a drop of about eight percent from his normal rate. He has compensated by throwing more changeups, which doesn't seem like a bad idea—his changeup is essentially an average pitch.
What's wrong with his fastball then? We can look at the PitchFX data, which measures velocity and movement in both directions. The data show that Guthrie's fastball movement is virtually identical to his career numbers.
In fact, the only pitch with significantly changed movement is his two-seam fastball, which he only throws 0.7 percent of the time.
So what's the issue? It's quite simple. Guthrie has been smacked around away from home and by left-handed hitters. This naturally led me to look at Guthrie's numbers in Yankee Stadium.
He pitched one game there, giving up 3 HR in 7 innings. The homers were hit by Robinson Cano, Melky Cabrera, and Nick Swisher. Guthrie isn't the first victim of left-handed hitting in Yankee Stadium.
An even stranger game occurred against Detroit, at Camden Yards. Guthrie pitched what looks like a gem—six innings, 10 strikeouts, one walk, three earned runs. Unfortunately, he also gave up two homers.
One of them was hit by left-handed batter Clete Thomas, who has reasonable power (career ISO of .130 or thereabouts), but nothing special. The other one was hit by the star CF Curtis Granderson, also a lefty.
Control isn't a problem, and neither is stuff. Gregg Zaun isn't stupid—I doubt he's suddenly asking Guthrie to throw tons of fastballs up in the zone or something like that. Anyway, Guthrie threw to Matt Wieters in his last start, giving up 6 ER in 0.2 IP (and, naturally, a home run to Jack Cust).
Can I pinpoint the reason? Not really. My first guess would be that it's just bad luck. Every pitcher has bad starts, and maybe Guthrie is just clumping them at the beginning of the year. I'm not a pitching coach, so I can't point to subtle differences in his pitches past what PitchFX tells me.
Even despite these problems, Guthrie has still accrued 0.2 wins of positive value according to FanGraphs. So at the very least, he's better than Jeff Suppan.