Despite a great year by Heyward, Buster Posey should win the award.
After getting swept by their bitter rival the Los Angeles Dodgers on June 30, the Giants proceeded to go 20-8 in July, highlighted by Posey's first month as a starting catcher, in which he batted .417 with seven homers, 24 RBI and 20 runs in just 103 at-bats. Not to mention a 21-game hitting streak, which tied a San Francisco Giants rookie record set by Willie McCovey.
When Posey entered the starting lineup, the Giants were in fourth place in the NL West, 5.5 games out of first. After just one month of Posey at the helm, the Giants were in second place, 1.5 games out of first, and had the third-best winning percentage in the National League. The Giants went on to go 52-33 since Posey's promotion.
Secondly, Posey—in just his first full year mind you—managed to take over as catcher seamlessly after Bengie Molina's departure and helped guide what was probably the best pitching staff in San Francisco's 52-year history. He quickly gained the talented pitching staff's trust and his cannon of an arm became known around the league.
What he did as a rookie calling the game could be the No. 1 reason he deserves the ROY in 2010. Rarely in baseball's history has there been a rookie catcher who commanded a game the way Posey did. Let's not forget he's still only 23 years old.
Third, the stats don't lie. Although Heyward had more RBI and runs (72 and 83 respectively) in 2010, he had 114 more at-bats than Posey and was a starter from day one for the Braves.
Posey hit the same amount of home runs (18) and batted .305 to Heyward's .277. He also managed to collect only five less RBI than Heyward despite his fewer at-bats. Posey hit his 18th home run in San Francisco's division-clinching 3-0 win over San Diego in the final game of the season.
Both players were stellar with runners in scoring position, with Posey barely edging out Heyward, hitting .312 to Heyward's .306. Posey had a higher OPS (on-base plus slugging), .862 to .849. Posey also only struck out 55 times the entire year, to Heyward's 128—a testament to how disciplined he was. Rarely did he look over-matched.
There's no doubt Heyward had a great year and will be a prominent player for years to come, but if Posey doesn't win the award this year, it would surely be a mistake.