The BBWAA announced today that they voted Florida left fielder Chris Coghlan the National League Rookie of the Year. While Coghlan had a great year, posting a .321/.390/.460 line and a .372 wOBA in 565 PA, he wasn't quite the best rookie in the National League.
That would be Andrew McCutchen.
Coghlan definitely had an impressive offensive campaign, he set the NL record for hits in a month in August, but he was also an absolutely awful defender in left field, posting a -14.5 UZR/150 and getting poor marks from numerous other fielding evaluations.
Meanwhile, Pirates center fielder Andrew McCutchen matched Coghlan's offensive performance, and did it while playing a solid center field. He posted a good .286/.365/.471 line and a .368 wOBA in 493 PA while posting a much lower BABIP than Coghlan, and he went 22 for 27 on steals, compared to 8 for 13 on Coghlan's part.
Given that McCutchen was worth approximately 16.7 runs offensively, compared to 20.7 runs by Coghlan (not to mention that Coghlan was luckier) it's clear that this was the criteria on which the BBWAA voted for Coghlan. Because had they shown any attention to defense, then there's no way that Coghlan would still win. Coghlan struggled to adjust to left field after coming up through Florida's system as a second baseman, while McCutchen showed off the athleticism that made him an elite prospect even before he was drafted, and it was reflected in his solid defensive metrics.
When you have two guys that offer similar offensive value, and one plays a very poor left field while the other plays a solid center field, then I don't see how you take the left fielder. That is, unless you just ignore the defense.