The thing about National League Championship Series Game 6 starter Kyle Hendricks is that in some very important ways, he's exactly the same pitcher he was last year, when he had a 3.95 ERA. His strikeout percentage of just over 22 percent is identical. His walk rate of just over seven percent is identical. Even his exit velocity is largely unchanged, since the gap from last year's 88.3 mph to this year's 87.2 mph isn't all that significant.
Toss in a small decrease in home run rate, and Hendricks' Fielding Independent Pitching (an ERA-like stat that looks only at strikeouts, walks, and homers) of 3.20 this year isn't far off of last year's 3.36. So: How in the world did he then cut his ERA nearly in half, from 3.95 to 2.13?
So what is it? The other things all matter, but there's one thing that really stands out. Let's look at Hendricks' platoon splits from last year and this year, and you see if you can tell the difference.
Hendricks against righties, 2015-16
2015: .223/.273/.307 2016: .196/.251/.305
There's a little improvement there, but not as much as you'd think; Hendricks allowed only four homers to righties last year, and nine this year. His strikeout percentage of just over 23 percent was identical.
Now let's look at lefties, and … oh, wow.
Hendricks against lefties, 2015-16
2015: .264/.325/.472 2016: .217/.277/.339
Now that's a difference, isn't it? Last year Hendricks allowed 13 homers to lefties, and this year only six. That's not something better defense or relievers can help with, and it's not like he faced markedly fewer -- 333 last year, and 319 this year. Remember before when we said his average exit velocity hasn't changed much? Overall that's true, but against lefties it's down from 88.6 mph to 85.9 mph.
So, how did he manage that? If you look at his pitch mixture just against lefties, some trends become clear. He's abandoned his cut fastball entirely. He's sliced his sinker usage in half. Suddenly, he's a guy who is primarily four-seam/changeup to lefties.
That's a move that makes sense. The sinker was ineffective against lefties (.321 last year, .297 this year), as was the cutter (.375 last year), and the changeup has always been Hendricks' best pitch, arguably the best change in baseball. Just look how it moves away from lefty hitters:
If you can do that, do that. Though it's got relatively high Statcast™ spin for a change, his consistent release point helps mask what it's going to do. Meanwhile, the four-seamer helped too. While the sinker didn't miss bats (10.7 percent whiffs per swing this year) and the cutter was hit hard, the four-seam was a nice weapon, garnering 19.5 percent whiffs per swing. Sometimes it's as simple as "take your best pitch and throw it more, while take your least effective pitches and throw them less."
There's more to it than that, of course. The defense did help, and Hendricks has located better as well, centering his four-seamer and changeup in a very tight location, low and outside to lefties.
Mike Petriello is an analyst for MLB.com and the host of the Statcast podcast. He has previously written for ESPN Insider and FanGraphs. This story was not subject to the approval of Major League Baseball or its clubs.