The pitcher with most HBPs is ... a reliever?!

Sometimes a statistic is so surprising, so shocking, so unbelievable that it's best just to get right to the point. So here it is:

The pitcher who leads MLB in hit batters, with 17 to be exact, is ... a reliever who has thrown all of ... 45 1/3 innings to date.

Yes, Padres setup man Austin Adams not only could approach the AL/NL record for most hit batters in a season in the Live Ball Era (since 1920), but he could do it while throwing barely 50 innings.

First, some context ...

Most HBPs in a Season (Live Ball Era)
Howard Ehmke: 23 in 279 2/3 IP in 1922
Roy Roberts: 22 in 245 1/3 IP in 1921
Kerry Wood: 21 in 211 IP in 2003
Tom Murphy: 21 in 215 2/3 IP in 1969

Two things jump out right away. One, this hit-by-pitch mark was established a long, long time ago -- almost 100 years ago, when the sport was entirely different from what it is now. And two, the lowest innings total among those four pitchers above? Try 211 by Wood -- or nearly five times as many frames as Adams has thrown this season.

Now, let's put this the other way around. As mentioned, Adams leads MLB with 17 HBPs. So what's the fewest innings in a season in which a pitcher plunked at least that many batters (since 1920)?

Fewest IP in a Season with 17+ HBP (Live Ball Era)
Austin Adams (17 HBP): 45 1/3 IP in 2021
Jerome Williams (17 HBP): 129 1/3 IP in 2004
Chan Ho Park (17 HBP): 145 2/3 IP in 2002
Charlie Morton (19 HBP): 157 1/3 IP in 2014

While these seasons are more recent than the previous list -- in part because the MLB-wide hit-by-pitch rate more or less has been climbing to an all-time high -- it's once again hilariously obvious that Adams currently has thrown only about a third of the innings that Williams did when he hit 17 batters in '04.

In case all of the above isn't yet mind-blowing enough, here's the twist: Adams actually is quite good. The 30-year-old right-hander sports a 2.58 ERA, a 1.08 WHIP (remember, that only counts walks and hits, not hit-by-pitches!) and a 13.3 K/9 rate in 56 outings after pitching in Wednesday's 16-inning marathon against the Dodgers.

How, exactly, does something like this happen? To answer that, we need to figure out who Adams is and what makes him the pitcher he's become.

Before going any further, let's clarify one thing. There are two players named Austin Adams who have pitched as righty relievers in the Majors in recent years. This Adams is the one who was drafted by the Angels in the eighth round in 2012, traded to the Nationals for Danny Espinosa in December 2016, then designated for assignment and dealt to the Mariners in May 2019, before being part of the seven-player Trade Deadline swap a year ago that sent catcher Austin Nola to San Diego and infielder Ty France and outfield prospect Taylor Trammell to Seattle.

This also is the Adams who, coming into this season had hit -- get this -- only two batters in his career (albeit in just 42 innings due to various injuries), and who deploys a wicked slider -- get this -- nearly 90 percent of the time. Yes, n-i-n-e-t-y.

This is the crux of Adams, whose spin rates on his slider and his fastball are among MLB's highest, which helps explain why he's been both wildly effective and effectively wild.

His slider is borderline unhittable: In his 45 1/3 innings, Adams has allowed only 21 total knocks (4.2 H/9). He's thrown the slider 687 times this year (out of 780 total pitches) and allowed only 20 hits on it. Against the offering, batters are hitting .149 (tied for third lowest in MLB) with a .187 slugging percentage (second lowest), including just five extra-base hits (all doubles). The 18.2 percent hard-hit rate off Adams' slider is the best in baseball, and that tracks with the fact that he has yet to allow a homer in 2021. He knows how to limit the damage, and that's an especially good thing in his case.

That's because Adams' slider also is pretty clearly difficult to control, given that he has walked 28 batters (5.6 BB/9) and -- you might've heard? -- hit another 17.

Adams admitted this season that earlier in his big league career, while with the Nationals from 2017-19, he was "kind of brainwashed with the old-school theory that you need to throw your fastballs for strikes. Then I came to understand that in the Major Leagues, getting outs is what matters. It's not about how you do it. ... And I didn't really get to figure out how good my slider was until I [got traded to the Mariners in 2019]."

That lines up nicely with the chart above, where you can see that Adams really began utilizing his slider at the expense of his four-seam fastball during the '19 season. He's just taken it to another level entirely since joining the Padres last summer.

So that's how Adams became the savage slider slinger he is today. But back to the hit-by-pitch aspect of all this, because that's the real fun.

You're probably wondering by now, "OK, so this Adams guy leads everyone in batters plunked, and he throws his slider practically all the time, but how many of his HBPs have come on sliders? It can't be all of them, can it?"

Oh, yes. Yes, it can. His near-singular slider is responsible for all 17 of the batters Adams has hit. Want proof? Count the yellow dots.

That's significant because it's already the highest total of HBPs on any individual pitch type in a season since pitch tracking began in 2008.

Most HBPs in a Season, by Pitch Type (Pitch-Tracking Era)
Austin Adams: 17 by sliders in 2021
John Lackey: 16 by four-seam fastballs in 2011
Daniel Cabrera: 14 by four-seam fastballs in 2008
Roberto Hernandez: 14 by sinkers in 2011
A.J. Burnett: 13 by curveballs in 2010
R.A. Dickey: 12 by knuckleballs in 2014
Charlie Morton: 12 by curveballs in 2021
Chris Sale: 12 by sliders in 2016
Doug Fister: 11 by sinkers in 2013
Jimmy Nelson: 11 by sinkers in 2016
Chris Sale: 11 by sliders in 2019
Justin Verlander: 11 by four-seam fastballs in 2008
Tim Wakefield: 11 by knuckleballs in 2008

So Adams has that "record" in hand. Given that he's averaged nearly 3.5 hit batters per month this year, it's very possible he could become the first pitcher to rack up 20 HBPs since 2004 (Bronson Arroyo and Carlos Zambrano) if he maintains that pace down the stretch.

As for that record total of 23 racked up by Howard Ehmke almost a century ago? Well, it's not as if Adams is actively targeting it. Then again, if his season has proven anything, it's that he doesn't always hit his target, but he still can leave a mark.