For the last several years, John Lannan has been a solid starting pitcher for the Nats. He has relied on a two seam (sinking) fastball to produce ground balls. Even when he has allowed runners to reach base, he has been able to get out of jams by inducing batters to ground into double plays. This year has been a different story, He's struggled to get batters to hit ground balls.
In 2009, 57% of the two seamers that Lannan threw broke 5-10 inches more than his four seam fastball. This year, only 43% of his two seamers have broken 5-10 inches more than his four seamer. As a result, batters are adjusting, and Lannan is getting lit up at the plate.
See the complete breakdown on my NatsStats blog here.