Hanrahan illustrates ERA illusion

Biggest turnaround this season?
Check out Joel Hanrahan.

In his first 34 games (and 33 innings), he posted 7.71 ERA.

In his second 32 games (and 30 innings), he's posted a 1.78 ERA.

What happened?

Two things, mostly.

One, he was traded by the Nationals to the Pirates.

And two, he's gotten a lot, lot luckier.

As a National, Hanrahan struck out 2.5 times more hitters than he walked. As you know, that's a perfectly acceptable figure. He gave up one home run every 11 innings; also a perfectly acceptable figure.

So how could he possibly have a 7.71 ERA? Well, he gave up a whopping .431 batting average on balls in play (prior to this season, he'd given up a .306 BABiP -- a perfectly average figure).

As a Pirate, Hanrahan's strikeout-to-walk ratio hasn't been as good ... but he hasn't allowed a single home run and he's given up just a .311 BABiP.

Hanrahan's not nearly as awful as his ERA with the Nationals; he's not nearly as good as his ERA with the Pirates (though his ERA cannot be explained simply by his BABiP). He's just another hard-throwing relief pitcher who might be excellent if he could walk significantly fewer hitters (but probably never will). He's also an object lesson at looking beyond ERA if you want a good read on how well a pitcher has actually pitched. And this is particularly important with relievers.