Searching For The Cause Of Kuroda's Regression

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Hiroki Kuroda's last 3 starts have been decidedly un-Hirok: 15 ER, 29 H, 5 HR in 16.2 IP.  The timing of this extreme regression obviously couldn't have been worse, and the Yankees need their new ace to right the ship sooner rather than later if they're going to have even the slightest chance of making a run in September.  Before he can do that, however, the source of the problem needs to be identified.  A comparison of his last 3 starts to the monster 5-game run he had in July sheds some light on what might be causing the downtrend.

From July 7th through July 31st, Kuroda gave up just 2 R in 33.0 IP, with 4 of those 5 outings being scoreless and not a single HR allowed.  Kuroda himself said his pitches have been flat in his last few starts, and a comparison of his PITCH/f/x stats from those 3 games and 5 in July confirms that.  His pitches have had less vertical and horizontal movement almost across the board in his last 3 starts, and a quick check of the side pitch trajectories from his last 3 starts compared to the 5 in July shows less of a downward plane and a noticeable upward shift in where some of his pitches are crossing the plate, particularly his splitter.

The results generated on his pitches in the last 3 starts have been in line with the "flatter ball" theory.  He's thrown his splitter and sinker for fewer strikes than he did in July and has seen his whiff rates on those 2 pitches and his slider decrease, dramatically in some cases.  The splitter has been especially easier to hit, going from a 22.2% whiff rate in July to just 9.4% in the last 2 weeks.  If those pitches are being delivered with less movement and coming across the plate in a better area to hit, batters aren't going to be swinging and missing much and they'll have a much easier time squaring Hirok up like they have been.

The good news is that there hasn't been a decrease in velocity.  In fact, Kuroda's velocity in his last 3 starts has been a tick better than what it was when he was shutting shit down in July.  If fatigue is the root cause of this rough patch, it's not translating to diminished velocity.  There doesn't appear to be a big difference in his release point from July to today, although not having the ability to watch multiple starts in a short span of time, I'm admittedly not qualified to comment intelligently on any changes to his mechanics.

The overall picture presented by these 2 PITCHf/x samples is a pitcher who's just lost the feel for his stuff, which I guess is better than a tired pitcher who just can't generate the velocity and spin he needs to be successful.  In theory, this is something Hirok should be able to work out in his between-start throwing sessions, and that should inspire hope that he can turn things around next month.