This significant drop-off, more than 100 BB per team from 2000 to 2005, came despite the fact that teams are preaching patience more than ever, in the wake of "Moneyball," and players like Barry Bonds, Jason Giambi, Adam Dunn, and Jack Cust made their livings largely by moseying slowly to first. Hitters adjusted to the new zone, still took their walks when appropriate, but were forced to swing at chest-high pitches, which no doubt quickened the pace of games and relieved the pressure on pitchers, even if it didn't cost the league any run production. There is evidence to suggest that the trend is heading back in the wrong direction, since the low-point in base-on-balls in 2005. The modest increases the past two seasons may foreshadow a significant upswing on the horizon. I, personally, feel like pitchers have been getting squeezed more often in games which I've been watching and the early numbers this season suggest that it isn't merely coincidence. In April of 2007, the average major league franchise took 87 free passes. This April that number jumped to 97. That's a total of 300 walks more across the league than a year ago (This number is somewhat exaggerated by the fact that there were more games in March this season). Nonetheless, taking into account March and the first few days of May, the current pace would result in an MLB average for the season of around 563, more than 20 more walks per team than any season since 2000.
I, personally, think Selig or Alderson would do well to issue a reminder to the umpires, in order to protect the fragile arms of major league pitchers.