This idea would seem ludicrous to many, who have observed that Chad Qualls has an ERA of 6.59 during his time with the Pirates, and one of over 7.00 in September. But then, Joel Hanrahan had an ERA in the 7s—when the Pirates traded Sean Burnett for him.
That is because something told management that Hanrahan (and presumably Qualls) was a much better pitcher than those numbers suggested.
That "something" was FIPs, or what we call sabermetric ERA.
That is a formula that estimates what a pitcher's ERA should have been, given certain other statistics like home runs, bases on balls, and strikeouts.
Using these metrics, Qualls is a good pitcher. During his tenure with the Pirates (13.2 innings), he has given up NO home runs, walked only two, and struck out six batters.
He doesn't even give up an inordinate number of hits. The measure of this is batting average of balls in play (BABIP).
Qualls' is .280, slightly less than the norm of .300. Given this fact, and his few walks and no home runs, his ERA should be lower, not higher than average.
So why is his ERA so high?
Qualls has strange pattern. He retires the side every OTHER outing. And on his bad nights, he gives up patterns of hits that wouldn't ordinarily turn into runs.
One run on two singles, because the first one was followed by a stolen base, before the second single. A solo double that turns into a run—because it is followed by two sacrifices.
In one case, after a double and two singles scored one run, Qualls was lifted for a reliever that gives up a hit that knocks in two more runs.
In other words, Qualls seems to give up an average number hits in "bunches" that produce a lot of runs.
But once you get over the problem of "small sample size," such bad streaks aren't supposed to happen to a pitcher too often.
The theory is that hits fall randomly (unless there are complicating factors such as a pitcher being injured). If this is the case, Qualls has been the victim of a "perfect storm" of hits falling in clusters.
Quall's FIP of 2.66 is actually lower than Hanrahan's 4.45, even though the former's ERA is much higher.
Maybe Qualls is a bad pitcher. but more likely he was unlucky.That is to say that if Qualls' (and Hanrahan's) hits start falling into more normal patterns that reflect their other statistics, Qualls' ERA should "cross" Hanrahan's by falling below it. (Statistics courtesy of FanGraphs.)
In trading (lucky) Sean Burnett for him, the Pirates rightly took a chance that Hanrahan's bad statistics were unlucky. They should probably feel the same about Qualls.
And even for those who don't believe that Qualls is basically a good pitcher, here's a scarier thought: Can Hanrahan's performance catch down to, or below Qualls? Because sabermetrics says that this has already happened.