Trevor Cahill had a fantastic year for the Oakland A's in 2010. He was very successful in keeping the ball down, as he went from a 96 ERA+ in 2009 to a 136 ERA+ last season. Some have noted that his very low overall BABIP (.237) is partially responsible for his success, rather than any particular ability to induce weak ground balls. However, a closer look possibly indicates that luck may not have played as big a role in Cahill's success.
Cahill was one of the most successful ground ball pitchers in the majors; 56% of batted balls off his pitches ended up on the ground in 2010, 5th highest in the majors. As you can see from the heat map above, he became very efficient at keeping his pitches down last season. His GB/FB ratio went from .92 to 1.32 in one year. The main reason: his excellent sinker.
Cahill's 2010 sinker was flat out nasty, averaging 14.8 feet per second of downward movement, putting him in the top 10 percent of sinkerballers. This makes it tougher to chalk up his basement low .153 batting average on ground balls (best in the majors) to mostly luck. He's obviously benefitting greatly from the movement he's getting on his sinker. If batters are finding it harder to makes solid contact as a result of that increased movement, it's possible they are hitting weaker ground balls; in turn, this would make it easier for his defense to field and turn these ground balls into outs.
This is not to say that we won't see some regression this year. It's certainly possible that a good chunk of these ground balls were simply finding infielders, particularly when well hit. But if he can keep his pitches down and moving as they did last year, don't be surprised if his overall BABIP remains in the cellar.