Depending on your statistic of choice, you can start quite the argument about Zack Greinke.

1. Zack Greinke is the best pitcher in baseball. He out-pitched every starter on the Phillies or Giants this year on his way to a historically good season.
   
   
2. Zack Greinke is overrated -- a pitcher who has thrown 391 innings over the past two seasons with a 4.02 ERA, and who isn't especially close to being an ace.

The claim for the first statement lies in xFIP, which is a statistic that's mostly concerned with a pitcher's walks and strikeouts. The claim for the second statement is something your Uncle Gerald says right before telling you that the Brewers should trade Prince Fielder and a draft pick for Troy Tulowitzki. The top ten pitchers in either league, as determined by xFIP:

Zack Greinke - 2.56
Cliff Lee - 2.68
Roy Halladay - 2.71
Clayton Kershaw - 2.84
Cole Hamels - 3.02
CC Sabathia - 3.02
Madison Bumgarner - 3.10
Justin Verlander - 3.12
Felix Hernandez - 3.15
Yovani Gallardo - 3.19

Greinke's at the top. He was better than any pitcher in the game if you give him credit just for the things he can control (per xFIP, anyway). He had a pretty special season by this metric. Since 1901, there have been ten seasons in which a pitcher has qualified for the ERA title, struck out more than 10.5 batters per nine innings, and walked fewer than 2.5 batters per nine innings.

So there have been nine seasons other than Greinke's, but only three other pitchers who have done it: Randy Johnson, Curt Schilling, and Pedro Martinez. All of them were considered aces at the time. Actually, for most of those seasons, they were all hyper-aces.

Except for Greinke.

And in all of those seasons, the pitcher didn't just finish the season with Cy Young votes, they all finished with MVP votes. But the Cy Young votes were the ones that added up. Schilling's fourth-place finish in 1997 was the lowest finish of the bunch. The other eight seasons featured four second-place finishes and four Cy Young Awards.

Well, the eight seasons other than Greinke. 

It's not a perfect comparison just to lineup strikeouts and walks across the years like this -- a 3.83 ERA means something totally different in 2011 than it did in 2002, as does a 10.00 K/9.

But the overall point stands. When a pitcher walks as few batters as Greinke did, and allows as few balls in play, he shouldn't just have a good season. He should dominate. He should pick up MVP votes. Instead, he finished with a higher ERA than any other National League pitcher to start a playoff game this year -- higher than those of Joe Saunders, Kyle Lohse, and Randy Wolf. 

Is he better than his ol' outdated ERA might indicate? Yep. Almost certainly. But there's a small part of me that wonders if he's the outlier, the one guy that xFIP just isn't capable of reading correctly, the pitcher who can't help but allow a home run at the exact wrong time. Or considering that shiny 16-6 record, maybe he's just a latter-day Jack Morris, pitching to the score!

Whatever the true talent level of Greinke is, he'll be the center of attention in Game 5. Brewers fans can take heart by noting how dominant his peripherals suggest he really is. Cardinals fans can take heart by noting that Greinke was closer to Jake Westbrook this season than Roy Halladay when it came to preventing runs. Greinke is all things to all people, an overrated underrated pitcher for the ages, and how his season is remembered might have a lot to do with Friday night's game.