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The mystifying Kyle Hendricks home run problem

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A look at the numbers behind a troubling trend

Kyle Hendricks walks to the dugout after giving up four home runs in the first inning against the Braves
Kamil Krzaczynski-USA TODAY Sports

There are very few certainties in life. Death, taxes and Kyle Hendricks just getting guys out by inducing weak contact with plus command and masterful deception are about as close as Cubs fans have been able to get the last few years. Well, at least until 2021 came for Kyle Hendricks, who has not looked like himself so far this season.

With any luck. everything that follows is just small sample size noise and in June and July we will all look back on the time that Kyle Hendricks was one of the worst starting pitchers by HR/9 and laugh, but it’s such an anomaly for a pitcher who has managed to keep his HR rate down through various iterations of superballs that it is worth taking a closer look at what exactly is going on here. Oh, and that wasn’t hyperbole — below is a list of the 10 starting pitchers with the highest HR/9 rates and at least 10 innings pitched, through Tuesday:

Bottom 10 pitchers by HR/9

Drew Smyly ATL 3 15 9.00 1.80 3.60 0.231 33.3% 23.1% 7.20 6.89 4.69
Griffin Canning LAA 3 12.2 10.66 3.55 3.55 0.313 33.3% 35.7% 8.53 7.04 3.82
Kyle Hendricks CHC 4 19 8.53 3.79 3.32 0.275 36.8% 31.8% 5.68 7.57 4.78
Patrick Corbin WSN 4 16.1 7.71 5.51 3.31 0.34 36.4% 27.3% 10.47 8.36 5.92
Matt Moore PHI 3 11 9.82 7.36 3.27 0.382 37.8% 23.5% 9.82 8.09 6.04
Mike Foltynewicz TEX 4 22 9.00 2.86 3.27 0.222 35.5% 28.6% 5.32 6.77 4.25
Jorge Lopez BAL 4 17.2 9.17 3.57 3.06 0.261 46.2% 35.3% 8.15 6.83 4.08
Domingo German NYY 3 13 9.00 2.08 2.77 0.349 42.6% 20.0% 6.23 5.78 4.45
Triston McKenzie CLE 3 13 12.46 6.92 2.77 0.269 13.8% 22.2% 4.85 6.63 5.03
Starting pitchers with at least 10 IP FanGraphs

This is not a list anyone would want to be on, but for Hendricks, who has never had a HR/9 over 1.11 (last year’s shortened season) it’s particularly perplexing. Hendricks has built a career off of an above average ground ball percentage and an elite ability to limit hard contact. Neither of those has been true so far in 2021. Let’s take a look at some of Hendricks’ batted ball and Statcast numbers by year:

Kyle Hendricks select stats by year

Season IP BBE GB% Barrel % EV Hard Hit %
Season IP BBE GB% Barrel % EV Hard Hit %
2015 180.0 521 51.3% 3.1% 88.0 29.2%
2016 190.0 523 48.4% 3.1% 86.6 26.0%
2017 139.2 405 50.1% 4.2% 85.0 29.1%
2018 199.0 598 47.0% 5.2% 86.4 30.6%
2019 177.0 539 41.3% 4.6% 86.5 31.4%
2020 81.1 242 47.1% 4.5% 86.2 31.0%
2021 19.0 58 36.8% 15.5% 87.3 36.2%
Batted ball and Statcast data FanGraphs

A few different things are happening at the same time in 2021 and none of them are good for Hendricks. First of all, his ground ball percentage which has generally been over 45 percent, and occasionally hit over 50 percent, is currently 36.8 percent. He’s distributing the remaining contact pretty evenly among line drives and fly balls and those balls are getting hit a lot harder than Hendricks’ pitches have been hit in the past. A 1.1 mile per hour change in exit velocity may not seem like a lot, but it’s contributing to a barrel rate that is more than three times higher than Hendricks has ever given up in his career. For those of you who aren’t Statcast types I’ll put it differently. In 2020 Hendricks allowed 10 home runs across 81⅓ innings and 242 batted ball events, in 2021 he’s already served up seven in 19 innings and 58 batted ball events.

There are a few different places we can look for explanations of what might be going on, let’s start with the usual suspects — velocity and location. Hendricks’ velocity is down about 1 mph on his four-seam fastball, but it’s in line with previous Aprils in his career, so it seems unlikely that is the reason his fourseam is suddenly so hittable. And make no mistake, Hendricks’ four-seamer is currently being hit hard — opponents are slugging 1.143 against that pitch. For reference, opponents slugged .348 and .302 against Hendricks’ four-seamer in 2020 and 2019, respectively. Since velocity seems in line with his historic norms, I wanted to take a look at location. Here are graphs of each of Hendricks’ pitches and their location from 2020 and 2021 courtesy of Statcast:

Pitch by pitch heat maps 2020
Pitch by pitch heat maps 2021

Hendricks’ location doesn’t have the same precision at the start of 2021 that he’s demonstrated in previous seasons and you can see that in the above comparisons. Hendricks himself reported “everything was flat” after his four-inning outing against the Braves on Sunday Night Baseball that included as this piece from the Athletic notes:

“Everything was flat,” said Hendricks, who maintained his daily throwing program except for Tuesday, when he was supposed to face the Brewers in Milwaukee. “It’s like any adverse situation. You just try and learn from it, feel what’s going on, but then forget about it and move on to the next pitch.

“I just made a lot of bad pitches there, a lot of flat pitches over the middle of the plate. Just got to set a better tone, be aggressive, come right at guys and get ahead in counts.”

One x-factor that is worth keeping an eye on is the baseball itself, which we know MLB changed for 2021 in an effort to contain exploding home run rates. Just after Spring Training Ben Lindbergh and Rob Arthur at The Ringer reported that one of the unintended consequences of changing the ball was that pitches were moving more than they had previously. On Monday, Devan Fink at FanGraphs noted that pitchers across the league are attacking the zone more with fastballs due to the new ball, although admittedly that analysis focused on flamethrowers throwing 95 mph and higher, which certainly does not include Kyle Hendricks. That said, it does seem worth exploring whether slight changes in the ball have impacted pitchers who rely on pinpoint precision, like Hendricks.

It is early in the season and a lot of weirdness can happen with small sample sizes. Hendricks has a track record of rebounding after poor starts like this forgettable game against Cincinnati in 2019 that barely moved the needle on a more-than-adequate season from Kyle where he put up a 3.46 ERA and only gave up 0.97 HR/9 despite home run rates surging across baseball. It’s entirely possible whatever contributed to this early home run spike is already fixed. But small sample size or not, it will be worth keeping an eye on Hendricks as he toes the rubber tonight in Atlanta.