Originally Posted by Wonderful Monds
It's gonna be because of the HR/FB discrepancy. To be honest I'm not the biggest fan of xFIP because assuming every pitcher can put up HR/FB numbers in the same ballpark is a pretty hefty assumption to make.
While pitchers HR/FB rates do vary between pitchers with lots of innings pitched in a career (so the small sample size argument doesn't work), they aren't that extreme. Without looking it up, they tend to range between 9-11% IIRC (some of which might be attributable to ball park effects).
If Leake is at 16%, you should expect that to regress somewhat. But he's always had a higher than normal rate.