A year ago, Mark Buehrle ended up in a place that was perfect for him. The NL East has strong pitching, and while the lineups are good, they aren't juggernauts. Throw in that his new park was expected to be pitcher-friendly, and just about everything was going his way.
So much can change in a year, though, and Buehrle is now out of this dream environment, and in one that could cause him problems. It's not going to kill his value entirely or anything like that, but it might knock him out of the running in many mixed-league formats.
Buehrle posted a 106 ERA+ last year, in 202 innings with the Marlins. Miami's new park was mostly neutral in its first year, and Buehrle ended up somewhat susceptible to home runs, giving up 1.2 per nine despite the move away from a stadium that boosts homer rates. He succeeded thanks to his consistently excellent walk rates, though, as well as one very important thing he will no longer have access to: opposing pitchers.
Buehrle held #9 hitters to a .087/.113/.130 line in 2012. As he was in the NL, most of these 81 plate appearances were those of pitchers. Starting pitchers hitting are taken advantage of by all pitchers in the NL, but Buehrle was well ahead of the NL's pace of .173/.223/.244. With the designated hitter in play, and more balanced lineups where the #9 slot hit .233/.229/.349 as a unit in the AL, Buehrle might be in a little bit of trouble relative to his recent past. Not significant trouble, but enough to put a dent in some of his fantasy value.
Throw in that he now has to face lineups he has historically had some issues against, and the idea he's going to be less valuable comes even more into play. In Buehrle's very successful career, the Red Sox have hit .300/.341/.453 against him, and the Yankees .333/.373/.498. The Red Sox might be a bit weaker than in their better years offensively, but if Buehrle comes to Fenway when the lineup is healthy, and has to take on Jacoby Ellsbury, Dustin Pedroia, David Ortiz, and Will Middlebrooks all in a row, bad things are still likely to happen to him. Same goes for the Yankees, who, despite their age, are still a prolific run-producing squad, playing in a park that doesn't favor pitchers. The Orioles can hit, and have a park that boosts that fact. The Rays, though, tend to be susceptible to command-and-control oriented lefties like Buehrle, so at least the unbalanced scheduling will give him a reprieve.
Need more proof? Out of 74 pitchers in the NL with at least 100 innings in 2012, Buehrle had the 28th-lowest OPS against, at 756. His teammate Anibal Sanchez received similar benefits from his environment and schedule, coming in at #29 for his time in the NL. In the AL, five of the 10 loftiest OPS against came from AL East pitchers, and nine of the top 25. Buehrle is likely to be flipped to that area, rather than the inverse, in 2013. He might not have to face Toronto's lineup, but as stated, the others still exist.
In AL-only leagues, Buehrle is an obvious selection, even with these downsides. In mixed, though, since he already tended to give up a lot of hits, and doesn't rack up the strikeouts, he was iffy even in his better years. He's a good grab for late in this formats, in case he continues to defy expectations as he always has. But relying heavily on him might be problematic, as this is one arm with more value in the real world than the fantasy one.