The Yankees knocked around Zack Greinke last night, scoring seven runs against him in only two innings. Probably the most unusual thing about Greinke's brief (shortest start since 2007) outing was the number of free passes he allowed. In his 2 innings and 16 batters faced, Greinke allowed three walks and hit a batter - all of this without striking out a single batter. This coming from a pitcher with a K/BB near 9 coming into yesterday's game. Strikeouts and free passes are two things that are directly in the pitcher's control, so it's a good (albeit incomplete) thing to look at for evaluating a pitcher's success. Tom Tango's kwERA (strikeout-walk ERA) is an ERA estimator that only uses strikeouts and free passes (walks - intentional walks + hit batsmen) as inputs and converts the differential into an ERA-like number. The chart below shows Greinke's kwERA by start, with the horizontal axis being the NL average ERA.
You can see that before yesterday, Greinke hadn't had a worse-than-average game by this measurement all season. Greinke's still leads his league in kwERA by a lot at 2.12; Clayton Kershaw is next at 2.54.