Can Chris Stewart Fix Ivan Nova?

In his previous two starts, Ivan Nova gave up 16 earned runs and 21 hits over 10.1 innings pitched. After he called his recent slump bad luck, I compared the PITCHf/x numbers, as well as video of his mechanics. I came to the conclusion that Nova, with the intention of increasing velocity, was overthrowing his pitches. It resulted in balls that were released too early and lacked spin rotation, which was causing his pitches to fly up in towards the right handed batter’s box. Throwing pitches to a righties’ weak spot, down and away, resulted in balls right down the middle of the plate.

It all changed when Nova was matched up with backup catcher Chris Stewart. While he still showed some signs of overthrowing, Stewart called a game where this wouldn’t be an issue. The outcome was 7.1 innings of 5 hit ball, 2 runs, and 10 strike outs. It was Nova’s best start since June, and a vast improvement over his last two stinkers. He truly looked like a different pitcher in the August 11th outing, and I’d like to blame his new catcher.

Pitch Type	Avg Speed	Max Speed	H Mvt	V Mvt	Selection	Whiff Rate
Four-Seam (8/11)	93.57	96.5	-5.19	6.40	42 (40.0%)	4.76%
Four-Seam (8/6)	93.12	94.6	-4.74	7.02	37 (54.4%)	5.41%
Slider (8/11)	88.49	90.2	-1.86	3.31	13 (12.4%)	38.46%
Slider (8/6)	87.58	88.7	-1.52	4.53	4 (5.9%)	0%
Curveball (8/11)	80.83	84.4	2.76	-6.94	46 (43.8%)	17.39%
Curveball (8/6)	80.41	82.7	4.29	-7.14	21 (30.9%)	19.05%

The sample size of PITCHf/x movement is too small to inquire into this deviation between games, but the selection stands out. With Stewart behind the plate, the pitcher threw nearly the same amount of curveball as he did four-seam fastballs. Compared to his start on 8/6, with Russell Martin behind the plate, Nova mixed his repertoire much more in his last start, throwing a total of 59 breaking balls out of 105 total pitches.

The picture above may better demonstrate how Nova mixed his pitches more randomly between 8/6 and 8/11. This trend does not end in August, as you’ll see below, how his awful start on July 31st shows a similar pattern with Martin catching. This can be compared to his previous start with Stewart July 8th, where there is again much more deviation in speeds pitch by pitch.

Only 4 of his 23 starts have been caught by Chris Stewart, but in those 28.1 innings, he’s posted a 0.63 ERA, a 9.21 K/9, a 2.22 BB/9, and a 7.94 H/9. Opposite these numbers, with Martin catching, Nova’s posted a 5.45 ERA, an 8.05 K/9, a 2.84 BB/9, and a 10.74 H/9. If this type of success with Stewart’s continues, there is a case to be made that he should be Nova’s personal catcher.

It’s impossible to tell exactly why the pitcher has performed so well with the backup catcher, but it appears that the way Stewart calls a game varies distinctively from Martin. My theory is that mixing speeds in his most recent start prevented hitters from sitting on his fastball and slider when they were ahead of the count. By dropping a curveball in fastball counts, it allowed Nova some leeway with his control.

I’m not sold that this will continue, but I’m all for allowing the experiment to continue. After losing CC Sabathia, Andy Pettitte, and Michael Pineda, and with Hughes already racking up double the innings he threw last year, the Yankees need Nova to contribute to the rotation during the rough months of August and September. Can Stewart fix Nova?