The thing is, this isn't that far below his career norms:
Starting from his rookie year in 2009 -
ERA 3.96, 4.92, 4.75, 4.59, 4.32, 3.43, 4.92, 3.15, 4.67
WHIP 1.336, 1.389, 1.407, 1.531, 1.282, 1.231, 1.360, 1.009, 1.401
HR/9 1.2, 1.0, 0.9, 0.8, 0.9, 0.8, 1.3, 0.9, 1.7
The W-L and HR/9 are way out of norm, but a lot of his stats are fairly average for him.
He's a low #3, #4 type pitcher. Last year was the outlier.