What's the explanation for A.J. Pierzynski's 27 home runs?

There isn't much of one, at least which points to a good likelihood of anything close to a repeat. Perhaps the left-handed batter beefed up a little and altered his approach just a bit in order to staunch the drop-off in his fly-ball rate from the previous season. You won't find much of an explanation in the numbers on his Fangraphs page (unless you read a take on his season from one of the site's many writers, like Howard Bender's).

Pierzynski parlayed his walk year, spent in the baseball's top launch pad, into the heftiest contract of his career. He bested his previous lifetime high in the category (which came in 2005) by nine. Yes, catchers often experience spikes in power production late in their careers, and he moved to another fantastic yard, which serves as home to a team with a better lineup than the Chicago White Sox's. But Pierzynski, 36, probably didn't sacrifice a measly couple of points in his above-average contact rate in order to become a candidate to bat cleanup for the Rangers. We may come to find out that he is, but the odds aren't in his favor; fantasy owners shouldn't be expecting it, even if some are willing to pay more than usual for him.