A Comparison

Let’s play the old comparison game. I’m going to show you four pitchers, and then you have to determine which one is the best.

Pitcher A: 8 GS, 48 IP, 57 H, 19 BB, 27 K, 11 HR, 6.43 FIP, 6.56 ERA
Pitcher B: 8 GS, 50 IP, 53 H, 20 BB, 25 K, 9 HR, 5.86 FIP, 4.86 ERA
Pitcher C: 8 GS, 55 IP, 51 H, 14 BB, 33 K, 5 HR, 4.10 FIP, 3.07 ERA
Pitcher D: 9 GS, 67 IP, 53 H, 12 BB, 42 K, 6 HR, 3.69 FIP, 1.76 ERA

I know, I know, it’s not very hard, right? Pitcher A is terrible. He probably doesn’t belong in baseball. Pitcher B is nearly as bad, and is a replacement level pitcher at best. Pitcher C is a solid middle of the rotation innings eater. Pitcher D is pretty darn good, though maybe not quite as good as his sparkling ERA would suggest.

What do they have in common? All four pitchers are named Bronson Arroyo.

That’s Arroyo’s 2009 season, broken up into quartiles. His first eight starts of the season, he was an absolute disaster – one of the very worst pitchers in baseball. He improved to just being lousy instead of totally miserable in his next eight starts, but at that point, half the season was gone and his FIP stood at 6.14. That’s a 98 inning sample of below replacement level performance.

His last 16 starts, though? He’s been the exact opposite. His FIP stands at 3.78 since July 10th, as he’s gone back to throwing strikes, missing bats, and keeping the ball in the park. His first half could not have gone any worse – his second half could not have gone any better.

The obvious question is why? I don’t have any idea. I’m not sure Arroyo does either. There’s always a post-hoc explanation for stuff like this, but it’s hardly ever true. The reality is that pitchers are remarkably inconsistent. Arroyo never was as bad as he pitched in the first half, while he’s also not as good as he’s pitched in the second half.

If there’s a lesson to be learned from this, it’s that pitchers are flaky, and even things that a pitcher can control can vary widely over fractions of a season. 100 innings may sound like a lot, but given the extreme variations that pitchers can face, it’s really not.

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Dave is the Managing Editor of FanGraphs.

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And in the end he was about the same pitcher he’s always been. Breaking this stuff up into quarter seasons or even half seasons is fun, but you’re right Dave, it barely means anything other than showing you how a pitcher got to around what he’s usually like over the course of a season.