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If I were to ask which team has had the best pitching staff in the majors so far in 2009, I doubt many people would answer the Colorado Rockies, for two reasons.  One, "Rockies" and "best pitching staff" have never been connected in any sentence written since Denver got an MLB franchise in 1993, and two, they have a 4.54 ERA this year, good for only 23rd in the majors.  But according to Justin's implementation of tRA, the Rockies are ranked first, deserving of an ERA more like 3.70.

What do the adjusted stats like about the Rockies?  And do they really know what they're talking about?  Let's find out.

Adjusting ERA

ERA has a few problems as a measure of pitching performance, most notably that it doesn't separate pitching from fielding and doesn't take ballpark into account.  Given that the Rockies have a poor defense and play in the most hitter-friendly park in the majors, we definitely need to consider those effects.

By UZR, the Rockies have been 15 runs worse than the average team in 2009, which is consistent with their -35 run 2008 season.  Simply removing 15 runs from the staff's ERA brings it down to 4.33, which is 16th among all UZR-adjusted team ERAs.  That's still a bit higher than their 4.10 FIP, but within shouting range.

And then, of course, there's Coors Field.  It's not as hitter-friendly as it used to be, but still increases run scoring by 21% according to Terpsfan1's park factors.  Colorado's played eight more road games than home games so far this year (which is good news going forward) so we need to reduce their runs allowed by 8.7%, which is the weighted average of their road and home park factors.  That puts their ERA at 3.98, very close to the top five.  Not the best, but certainly quite good.

Of course, we haven't considered the fact that Rockies pitchers haven't had to face many designated hitters.  In general, an NL pitcher switching to the American League will see an ERA bump of half a run, meaning the Rockies team ERA would probably fall outside the top ten, but not out of the top half.

How Have They Done It?

For years the Rockies have tried to acquire talented ground ball pitchers and it seems they've finally succeeded.  The staff leads the majors in GB/FB ratio, and has managed to hover around league average at 10.5% of fly balls leaving the yard.  Even while playing home games in Coors, they've allowed under one home run per nine innings, good for tenth in the majors, thanks to all those ground balls.

The staff's strike out rate isn't stellar at 6.7 K/9, but that's to be expected given that the Colorado air doesn't help pitches break as much.  Their walk rate is quite good, at 3.2 BB/9, and their overall 2.1 K/BB ratio is tied for 8th in MLB.

Four-fifths of the starting rotation have been especially impressive, and the one-fifth isn't who you might think.  Ubaldo Jimenez, whom Tommy recently profiled, sports a 3.31 FIP, eighth best in the NL.  Jorge De La Rosa, despite a poor ERA, sits a 4.02 FIP and is striking out nearly 10 K/9.  Rays cast-off Jason Hammel sits at a 3.67 FIP and journeyman Jason Marquis is at 4.37.  Aaron Cook's been the worst starter, with a 4.80 FIP -- striking out 4.5 K/9 just isn't a recipe for success -- but that's still better than replacement level, especially in Coors.

Are They Really The Best Pitching Staff So Far?

Probably not.  Even using Justin's version of tRA instead of adjusted ERA or FIP leaves us needing to adjust for the DH factor.  However, the Rockies do, quite possibly, sport the best pitching staff they've ever had, one that rivals the Dodgers, Braves, and Giants for best in the National League.  As has been the case for a few years now, the strength of the Colorado team lies in their arms and not the position players who are overrated by their home park and some of who struggle in the field.  This is a good team, led by their pitchers, who should be in the NL wild card race into September.