2010 contained one of the best crops of rookies, especially in the National League, of recent years. Many of them, including Stephen Strasburg, Jaime Garcia, Starlin Castro, Ike Davis, Gaby Sanchez, Mike Stanton, John Axford, Jonny Venters, and many more, will likely become household names in the years to come as a new generation of superstars.

However, the two who, in most opinions, will shine the brightest for years to come, Jason Heyward and Buster Posey, had fabulous seasons, not just for rookies, but also as compared to players of all ages. As was just announced, Posey was selected as Rookie of the Year (ROY) for his efforts in leading the San Francisco Giants to a World Championship, narrowly beating Heyward of the Atlanta Braves.

Heyward was a top prospect that had been lighting the minor leagues on fire and made the club from Spring Training, while Posey was among an elite class of minor league catchers who hit for average and power, which included Carlos Santana of the Cleveland Indians and Jesus Montero currently of the Scranton/Wilkes-Barre Yankees, the AAA affiliate of the New York Yankees.

Let’s look at a stat line of the two during the regular season (Heyward is first):

142 623 520 83 144 18 72 11 91 .277 .393 .456 .849 131 237 4.4
108 443 406 58 124 18 67 0 30 .305 .357 .505 .862 129 205 3.0

A few things immediately stand out upon observing the stat lines. The first, and the most important observation, is the disparity in games, plate appearances, and at-bats. Those led to the gap in runs, hits, and total bases, which is due to Heyward making the team from the season’s start in April as opposed to Posey’s call-up in late May. Posey did offer more homeruns per at-bat than Heyward, but Heyward had enough speed to swipe 11 bags to Posey’s none.

The most accepted interpretation of the definition of the Rookie of the Year is a rookie who added the most value to a team. One sabermetric stat that attempts to quantify this is WAR, which is Wins Added over Replacement. Basically, if an arbitrary low-end player was in Jason Heyward’s place for the course of the season, the Braves would have won 4.4 less games. For Posey, that would have cost the Giants three games.

Keep in mind that both teams literally secured their playoff spots on the last day of the regular season, meaning both teams would have missed the playoffs, hypothetically.

In this debate, to argue for Buster Posey, some might argue with average-based statistics. Though Heyward’s batting average was significantly lower than Posey’s, his on base percentage (OBP) was a good bit higher, and it was enough for eighth in the MLB. Likewise, had Posey had enough plate appearances to qualify, his .305 BA would rank 18th.

Heyward’s high OBP was mostly due to his impeccable plate discipline, which accounted for 91 walks to Posey’s 30. Also, don’t be fooled by on-base plus slugging percentage. OPS+ is a more accurate stat which adjusts for ballpark differences.

With the average based-stats being incredibly comparable, the deciding factor becomes the gap in longevity, and therefore impact, on their respective ballclubs. Though his postseason presence was unquestionable, the postseason should not and is not be taken into account in the ROY. However, for the regular season only, Heyward unquestionably proved his worth.

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