Why do hitters rarely swing at first pitches from Kyle Hendricks?

On the super complete, first place Cubs team of destiny, Jake Arrieta isn't the ace. Jon Lester isn't the ace. Both are great, and both would probably earn the title of ace for a not so stacked team. But the Cubs ace, at least ERA-wise, is Kyle Henricks. Hendricks has been Kershaw-esque this year, and while FIP doesn't quite believe his low ERA due to his non-spectacular bat missing ways, there are reasons to believe his ability to limit hard contact is real.

Tied into Hendricks' great season is his ability to throw strikes and limit walks. He's 25th in the league in walk rate among starting pitchers, and throwing strikes has never really been an issue. Beyond walks, living in the zone effectively can give pitchers a leg up in terms of count leverage, which can help them reap huge rewards. Hendricks is second in the majors behind only lab experiment gone right, Clayton Kershaw, in terms of throwing first pitch strikes.

Do you notice the outlier on the chart above? Hendricks throws a first pitch strike in the vast majority of at bats, yet hitters are actually swinging less than league average on his initial offerings. This seems backward for two reasons: Obviously, hitters should be more inclined to swing when they're more likely to see a strike, and they're most likely to see a strike first pitch against Hendricks. Secondly, hitters often look to jump on early offerings from better pitchers. The pitchers with the highest first pitch swing percentage are often the best, yet Hendrick's is getting away unchallenged. What gives?

It's mostly unique to first pitches

An obvious question is the presence of this factor in other counts. Hendricks' overall swing rate is below league average, inducing swings only 43.8% of the time compared to a league average of 46.5%.

However, when we separate the first pitch numbers from the rest of his numbers, we get confirmation that Hendrick's first pitch numbers are indeed wonky. On first pitches, he's getting swings at an incredibly low rate of strikes per swing. On non-first pitches, that number nearly normalizes, sitting just a touch above league average.

Why is no one swinging?

Some theories:

-Some of it is undoubtedly due to excellent pitch framing, which the Cubs have in spades because of course they do. All three catchers that have seen significant time this year (David Ross, Miguel Montero, and Wilson Contreras) grade out as above-average framers, netting Hendricks a rather generous strike zone. So, some of the strikes hitters are letting go by would otherwise be balls.

-Per Bill Petti's Edge%, Hendricks ranks number one in terms of outside edge percentage of all pitchers who have thrown at least 1000 pitches. He doesn't have great velocity, so he's bound to work more away from hitters, and this year he's done so better than any other starting pitcher in baseball.

Petti's caluclations don't give us granular detail by count, but heatmaps indicate that Hendricks isn't spotting his first pitches with the precision that would induce takes. Put more simply, Hendricks has certainly thrown his fair share of pitches that without context, look absolutely appetizing.

-When I first discovered this trend, I thought the answer would be simple. Hendricks has a complete arsenal, throwing four pitches that rate above average by FanGraphs' pitch values. He can throw all four for strikes, and while normally hitters can go into the box looking for a fastball first pitch, Hendricks' arsenal is too diverse to give in early in counts. Right?

Except it's not really the case. Hendricks isn't a one-pitch pitcher to start at bats, but he does throw his sinker significantly more than any other pitch and significantly more than he does in other counts.

If anything, his arsenal is more predictable in those 0-0 counts. I'll head back to square one.

How big is the effect?

Quantifying the effect of stealing a first strike is hard to do. We can look at run matrices and know the difference in run expectencies in different counts, but truth is, there's too much nuance to game theory to fully appreciate what Hendrick's unique ability to get ahead means.

We can look at his numbers this year, and true to form for a Cy Young candidate, Hendricks has been good in every count. So while being ahead 0-1 is always preferable, being behind hasn't hurt Hendricks like it does most players.

We do glean some information from the chart above. Hendricks has been absolutely murder on hitters on first pitches this year, being a full 32% better than league average (sOPS+). So, hitters could be wary of those numbers, not wanting to have a short and futile at-bat.

It could be a less tangible factor based on those poor first pitch numbers; it's possible hitters just need a few pitches to adjust to Kendricks. The man does have a funky delivery, after all.

A mystery unsolved

At any rate, it's an interesting question. Kendricks doesn't seem to do anything special on first pitches, but hitters are letting strikes go by at a rate much higher compared to any of his counterparts. Often, we see hitters try to jump on early offerings from good pitchers to jump on early meatballs, but we're seeing the opposite here. It's a trend that's hard to explain and one that's certainly interesting to watch.

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Tim Eckert-Fong is a contributor to Beyond the Box Score.