Erick Aybar (LAA) hit well in 2009, posting a .312/.353/.423 slash line, good for a wOBA of .334. In 2010, that dropped to .253/.306/.330, a poor .282 wOBA. So far in 2011, Aybar's averages are back up. What changed from 2009 to 2010, and has it changed back?
Aybar is a switch hitter, with most of his at bats coming against right-handed pitching. In 2009, umpires gave Erick the benefit of the doubt on pitches on the inside corner of the plate.
Umps called strikes wide on Erick, but he could take the inside pitch, and force pitchers to move farther over the plate, a better hitting zone. In 2010, umpires were not as generous.
While he still got the low strike called a ball, the inside edge of the plate reverted rightfully to the pitcher. You can see how this might hurt a batter. He was hitting in pitchers counts more often, and right-handed opponents didn't need to move over the center of the plate as much. His strikeout rate against RHP went from 10.6% in 2009 to 14.6% last season.
What about in 2011?
Erick gets a big chunk of the lower, inside part of the plate. The upper inside edge still belongs to the pitcher. With almost one quarter of the zone going Aybar's way, it no wonder his slash line is back up to .342/.364/.425 and his strikeout percentage is now to 11.3%. I would be dubious of that much of the zone going his way the full season, but if can at least keep the lower inside edge, he might post good numbers again.