The Chicago Tribune's Paul Sullivan writes definitively that "[t]hough [Juan] Pierre was brought in for his offense, his defense also is supposed to be an upgrade from Corey Patterson, who regressed in the field his last two seasons as his batting average plunged."

There are two things wrong here. First, according to Baseball Prospectus's metrics, Patterson did not regress in the field in 2004-05. In fact, he became a league-average defensive centerfielder.

Admittedly, defense is still harder to measure than offense, and there may be metrics out there that disagree with Baseball Prospectus. But Sullivan doesn't explain the basis for his statement and he's the first person I've seen who has said that Patterson's defense had regressed the past two seasons.

The second thing wrong is that, while Pierre is a better offensive player than Patterson, he's not a better defensive player. Over their careers, they're about the same (97 Rate for Pierre; 96 for Patterson). But over the past two seasons, Pierre has been about 6 runs prevented per 100 games worse than Patterson.