We're at the point in the baseball season where all the two-week flash-in-the-pan performances have melted away and nobody is on pace for 100 home runs anymore.  But that doesn't mean all the numbers out there are for real, especially on the pitching side of the ball.

Some starting pitchers with pretty early-season ERAs are for real, and some aren't.  To separate the two, we need to look at peripherals, most importantly strikeouts, walks, and homerun prevention.  One nice estimate of a pitcher's demonstrated talent level is FIP, which takes those three skills and produces an ERA-like number on the same scale.  I like to think of FIP as "the ERA a pitcher deserved given the skills he demonstrated."

To produce the list of the ten most overrated starters (based on 2009 ERA) below, I went to Fangraphs, selected all the pitchers who had thrown at least 25 innings as of Sunday's games, and found the ten whose ERAs were the lowest relative to their FIPs (E-F).  Also listed is tERA, Stat Corner's advanced DIPS-style metric, as a backup to FIP.

1. Jair Jurrjens (Braves) -- 40.1 IP, 2.01 ERA, 4.34 FIP, -2.34 E-F, 3.97 tERA
   It's not that Jurrjens has been bad, it's just that he's not a stud.  Striking out 4.5 hitters per game and walking 3.5 per game is not a recipe for sustained success.  He was better than this last year, and should be an average to slightly above average starter going forward.  Just don't think he's found the secret to future ace-dom.
2. Matt Cain (Giants) -- 38 IP, 2.61 ERA, 4.92 FIP, -2.31 E-F, 4.47 tERA
   Dan Szymborski and I talked about Matt Cain a bit in our chat yesterday.  Yes, he's been historically unlucky with run support and his W-L record.  But the Giants also play in a stadium that's friendly to fly ball pitchers, and Cain's definitely a fly ball pitcher, meaning he's also lucky in some regards.  Anyway, giving up over one home run per game and sporting a 1.5 K/BB doesn't support a sub-3.00 ERA.  His career hom run rate is a bit better, but expecting an ERA much lower than 4.00 the rest of the way is a stretch.
3. Trevor Cahill (Athletics) -- 33 IP, 3.82 ERA, 5.85 FIP, -2.03 E-F, 7.33 tERA
   No, that tERA isn't a typo.  Cahill has a ton of talent and hitters aren't doing anything with his pitches when he puts them in the strike zone.  Unfortunately, he hasn't been able to find the strike zone this year, walking just under five batters per game.  Without any changes, he'll be out of the rotation soon.  However, if (and that's a big if, at least in the short term) he can put more balls over the plate, he would see his <1 K/BB rate rise, helping to offset the increase in BABIP he's likely to see.
   
4. Doug Davis (Diamondbacks) -- 44.1 IP, 3.25 ERA, 5.23 FIP, -1.98 E-F, 5.14 tERA
   Nobody can root against Davis, but giving up 8 home runs usually results in more than 16 runs allowed.  Going forward he'll probably give up fewer long balls and revert to the 4.25 ERA pitcher he's been for the past couple years.
   
5. John Lannan (Nationals) -- 39.1 IP, 3.89 ERA, 5.77 FIP, -1.88 E-F, 5.99 tERA
   It would be nice to say the Nationals have a bright spot on the pitching side of the ball, but 20 Ks against 15 BBs and 7 HRs isn't even a glimmer, let along anything bright.
   
6. Kevin Millwood (Rangers) -- 52.1 IP, 2.92 ERA, 4.63 FIP, -1.71 E-F, 5.16 tERA
   I root for Millwood, and walking under two hitters per game is impressive, but a Carlos Silva-like strikeout rate leaves too many balls put in play, especially ones that go over the fence.  As his tERA is right in line with what both his tERA and ERA were the past two seasons, an ERA around 5.00 is the most likely scenario the rest of the way.
   
7. Chris Volstad (Marlins) -- 42.1 IP, 2.98 ERA, 4.67 FIP, -1.69 E-F, 4.90 tERA
   Like the Marlins win-loss record, Volstad's early season numbers are a mirage.  A .231 BABIP on a team that doesn't field well in general isn't a sign of ERA sustainability.  His K/BB rate is good and if his 17% HR/FB rate can come down a bit, he'll be an above-average starter, just not a Cy Young contender.
   
8. Jered Weaver (Angels) -- 40.2 IP, 2.66 ERA, 4.31 FIP, -1.65 E-F, 3.42 tERA
   Here's a case where tERA disagrees with FIP by almost a full run, most likely because FIP regresses Weaver's .230 BABIP all the way, while tERA likes the fact that 18% of his batted balls are infield flies.  His 7/2 K/BB ratio is excellent, although because he's giving up more fly balls overall, his HR/9 may rise a bit, meaning one should expect good, but not great, stats the rest of the way.
   
9. Mark Hendrickson (Orioles) -- 26.1 IP, 5.13 ERA, 6.75 FIP, -1.62 E-F, 7.09 tERA
   When your ERA is over 5.00 and you've been lucky, that's not a good sign.  You don't need me to tell you that Hendrickson won't be a serviceable pitcher any time soon.  The only good news for Baltimore fans is that the faster Hendrickson's ERA flies north, the sooner they'll start to see the glut of Oriole pitching prospects called up to the majors.
   
10. Joe Saunders (Angels) -- 47.1 IP, 2.66 ERA, 4.23 FIP, -1.57 E-F, 3.05 tERA
    Saunders' ERA was well below his FIP for the 2008 season as a whole, and he's doing it again this year.  Like another Angel above, his tERA looks much better than his FIP, thanks to a 23% IF/FB.  Your choices are to think he can sustain producing an enormous percentage of batted balls that are infield flies, or being worried that a 4 K/9 will eventually catch up with him.  I'll take option two.  I do wonder, however, if there's a chance the Angels have an organizational philosophy towards inducing infield flies...
    

Here are some quick hits without much commentary.  I looked at the next fifteen or so players based on ERA-FIP and picked out those whose peripherals were the most scary: Mark Buehrle (decent K/BB indicates he's more of a high 3.00's ERA guy), Lance Cormier (the only reliever with 25+ innings is striking out less then three batters per nine innings and has given up home runs on only 3.7% of fly balls), Tim Wakefield (yes, knuckleballs are hard to hit, but his .228 BABIP and .23 HR/9 rates are bound to go up and will no longer hide a 1.4 K/BB ratio), Scott Richmond (his peripherals are average across the board, enough said), Aaron Laffey (more walks than strikeouts and only 4% of fly balls have gone for home runs), Roy Oswalt (what happened to all the Ks?), and Zach Greinke (his FIP is a lofty 1.46).