Tough choice for N.L. Rookie of the Year

As we wait for Game 3 of the Braves' and Giants' series, let us turn to a burning question: Who deserves the National League's Rookie of the Year Award?

First, I should mention that our answer won't be Jaime Garcia, who started 28 games for the Cardinals and went 13-8 with a 2.70 ERA.

It won't be Marlins first baseman Gaby Sanchez, who knocked in 85 runs. Or his teammate Mike Stanton, just 20 years old, who didn't debut until June but still hit 22 home runs in 100 games.

It won't be shortstop Starlin Castro, who came up in early May and batted .300 on the nose while anchoring the Cubs' middle infield for the rest of the season.

It won't be first baseman Ike Davis, who hit 19 home runs and was one of the few bright spots in the Mets' otherwise miserable season.

In a typical season, all of these talented young fellows would rank as excellent Rookie of the Year candidates.

Not this season, though. This season, they'll all be fighting for that coveted third slot on the ballot. This season, the award is all about Buster Posey and Jason Heyward.

Heyward, of course, took a big (and ridiculously) early lead in March, when tales of his prodigious feats -- some of the tales tall, some not -- filtered from spring-training camps in Florida to computer screens throughout America. Meanwhile, the Giants' decision-makers convinced themselves that Posey, their No. 1 prospect, needed more seasoning in the minors.

By the time Posey reached the majors in late May, Heyward ranked as one of the best players (let alone rookies) in the National League, with nine home runs, 35 RBI, and a .295/.422/.568 batting line.

At that point, Heyward was essentially the only Rookie of the Year candidate and Posey didn't even qualify as an afterthought.

Baseball's a funny thing, though: things change. And boy, did this thing change.

Heyward struggled terribly in June, then spent a couple of weeks on the disabled list. Meanwhile, Posey started hitting immediately -- he collected six hits in his first two games -- and never really stopped. Even though Heyward did just fine after returning to the Braves' lineup in mid-July and Posey didn't play nearly as much as Heyward, they finished almost exactly even in both home runs and RBI.

For that reason, Posey has caught and perhaps passed Heyward in the Rookie of the Year sweepstakes. Leaving aside the home runs and RBI, though, it's awfully hard to argue that Posey has created more runs than Heyward. Their OPS's are roughly the same -- Heyward's got the higher on-base percentage, Posey the higher slugging percentage -- but Heyward's OPS came in 623 plate appearances, as opposed to Posey's 443.

As these things go, 180 plate appearances is a pretty big difference.

Over at FanGraphs, Heyward finished ahead of Posey in Wins Above Replacement, 4.9 to 3.9.

At Baseball-Reference.com -- where they use a slightly different version of WAR -- Heyward also finished ahead of Posey, 4.4 to 3.0.

Nevertheless, Posey's got a lot of supporters, and one of their arguments is that the Giants wouldn't have reached the playoffs without him.

Which is true. And it's precisely as true about Heyward. If the Giants had won just two fewer games, they would have missed the playoffs. The same is true of the Braves. The same is exactly as true of the Braves. You simply can't use the "without him, they wouldn't have made the playoffs" argument to push Posey past Heyward. It does not work.

Fortunately, there's another argument available, and it's got the virtue of being almost impossible to refute.

See, there's one thing we still haven't really figured out: how to measure a catcher's defensive contribution. In Posey's case, he did a pretty good job against the enemy running game, saving (by one measure) three runs.

That's not the argument, though. The argument is that the Giants' pitching staff performed significantly better once Posey took over behind the plate. And it did perform well.

But you might recall that Posey didn't join the Giants until late May. Well, he didn't become the Giants' regular catcher until more than a month later; before the 1st of July, Posey started behind the plate just twice. So we're talking about three months.

Again, the staff did perform well in those three months. From April through June, the Giants' team ERA was 3.46; from July through the end of the season, the ERA was 3.28.

OK, so that's not a huge difference. Posey's supporters might point to the Giants' 1.90 ERA from the 1st of September through the end of the season, but doesn't the 4.55 ERA in August count, too?

The bottom line, for me, is that Posey started only 75 games behind the plate for the Giants. I get the impression that his fans want to give him full credit for the Giants' impressive pitching stats, when a) he played only half the time, and b) Tim Lincecum and Matt Cain were pretty good pitchers before Posey showed up.

If Posey had caught 25 more games -- or maybe if he'd just played 25 more games -- I probably would vote for him. That's not what happened, though.

I don't think there's a wrong answer here. I really don't. I just think that Jason Heyward is ever so slightly more right.