Most of the world has now stopped considering Mike Pelfrey an "ace", which is cool, since nobody knows what that means anyway, or why that label would be applied to Big Pelf of all people. But after another crummy start, you can still hear a faint grumbling from Mets fan wondering what happened to Pelfrey, who, after starting opening day, is only the Mets fifth best pitcher. Of course, Pelfrey's "terrible season" has a lot more to do with our own biases than his actual results, which are bad but not terrible on an epic scale. In short, it's probably time we start being happy with the Mike Pelfrey we have, rather than the Mike Pelfrey we want.
For sure, the big guy has not been good. But even his down year isn't as down as you think, and his up years weren't as up as you think. And you probably know all this. But to summarize briefly, a lot of the argument against Pelfrey as a very good pitcher centers around advanced stats, which tend to rely on strike outs as a measure of effectiveness. Pelfrey doesn't strike guys out. So, while Pelf has had wild fluctuations in ERA throughout his career, his FIP has varied less and his xFIP basically not at all (all data from Fangraphs).
But you don't need advanced stats to see that Pelfrey should never be considered a lock for a good season. I don't know why anyone would believe a guy whose had career best ERA's of 3.72 and 3.66 doesn't stand a good chance of posting a 4.67 ERA any given year. In fact, Pelfrey's cumulative ERA in 2008-2010 was 4.11, not terribly different from his 4.67 mark this season.
And if you are looking for statistical evidence that Pelfrey is in fine shape long-term, he's striking out more guys per 9 than he did last year (or in 2009) and walking less than at any time during his career. He is giving up a lot more home runs, more than twice as many per 9 as last season, which is bad, but for all we know this could be a fluke, or just a stretch of ineffective pitching that will have no bearing on the future.
If you want to look into some or the more advanced numbers, take his pitch type values (via Fangraphs, again), and you'll see a lot of variability across his career. In 2008, which many would consider his best season, his fastball was extremely valuable, and his curveball, slider and change all stunk. But then in 2010, his second best season, his fastball was good (but not as good), and his curveball was pretty good. This season, none of his pitches rate well, in particular his curveball, but it bears mentioning that his slider is better than a season ago, and his fastball is a lot better than it was in 2009. I don't pretend to have the expertise to read a ton into this numbers, which seem arbitrary to my eyes. The big statistical red flag would seem to be that Pelfrey is throwing his slider a lot more than he did a season ago, and that his fastball has continued its downward slide in velocity. But I'd imagine that Pelf's bad season is as much a matter of perception and expectations as it is poor results.
Pelf came up through the system, arriving in the majors throwing 95mph, standing 6'7" with first-round pedigree. He's a quirky guy. We like him. Hell, I own a Go Big Pelf t-shirt. And man is he infuriating. He's the kind of guy who seems perpetually a step away from getting "there," whether it be finishing off a batter, an inning, a start or vaulting himself into the territory of very good, or even elite, pitchers. But that's on us, not Pelfrey. In reality, there's no more reason to believe Pelf will take that next step any more than dozens and dozens of other pitchers throughout baseball. Most of those guys won't end up as really good pitchers, and neither will Pelfrey, in all likelihood. It's about time we accepted Mike Pelfrey for who is he.