Cole Hamels of the Philadelphia Phillies reduced his hits and home runs allowed this season to put him in Cy Young contention. He accomplished this by inducing more ground balls with his fastball. From 2008-2010, the percent of ground balls and fly balls put in play against his fastball were very similar, 30.5% fly balls, 35.2% ground balls. On fly balls, batters did very well, with a .297 batting average and a .814 slugging percentage. On ground balls, they did poorly with averages of .236/.263.
Note that in this time period, Cole's fastball stayed up. Compare that to 2011:
Not only is his fastball lower in the strike zone, his movement is a bit farther toward right-handed batters. He's now getting 46% of his balls in play as ground balls, only 24.9% as fly balls. The fly balls still give batters good results, .297/.734. Batters are hitting .262/.295 on ground balls, but it's worth it to keep the ball in the park. Hamels is trading extra-base hits for singles, a trade that is paying huge dividends.