The Best Reliever in Baseball

If you are a casual baseball fan, you probably can’t rattle off the names of too many Milwaukee Brewers’ middle relievers. For the most part, I don’t blame you. After all, the Brewers aren’t often featured on national broadcasts and as a team playing in a small market in a Midwest city, they tend to be an afterthought in the mainstream baseball discourse. Despite challenging the Cubs for the NL Central crown for the better part of 2017 and making some splashy offseason acquisitions, the Brew Crew still probably doesn’t get the attention they deserve.

And so it follows that if a team is being underappreciated, the already overlooked middle relievers on such team are especially neglected, even when one of these relievers is putting up historical numbers. This reliever’s name is Josh Hader, a left-handed phenom whose video-game like numbers force me to double take and refresh the page every time I take a look at his stats.

Before I dive into just how amazing Hader has been in his first 59.1 major league innings, I should probably provide some background on Hader’s unique place on the Brewers pitching staff. Throughout the minors, Hader was being groomed as a starting pitcher. Over five seasons, Hader made 95 starts and posted a 3.25 ERA, solidifying himself as one of the best pitching prospects in the game. However, last summer, as the Brewers found themselves in the thick of the NL Central race, the club decided to put his development as a starting pitcher on hold and call him up to the majors to pitch out of the bullpen.

While the Brewers recognized Hader’s enormous potential, not even they could anticipate the dominance that would ensue. In 35 games down the stretch, Hader posted a 2.08 ERA while striking out over 12 batters in an inning and quickly settled into the multi-inning Andrew Miller-type fireman role, helping bridge the gap in front of All-Star closer Corey Knebel.

Ironically, Hader might have been too dominant for his own good. Due to the fact that Hader was so lights out in the bullpen, the Brewers decided to keep him in the same role this season. I am sure if you asked anyone in the Brewers front office, they would tell you that the long-term plan is for Hader to transition back into the rotation, but since he has established himself as such an integral bullpen piece, it appears those plans will be put on hold for the time being.

In an era where rigid bullpen roles are rapidly losing favor, Hader’s ability to come into any situation and throw multiple innings has vital for a club that is desperately searching for any way to get outs from its relief corps. The fact that Hader was groomed as a starting pitcher gives him the longevity necessary to be utilized to flexibly by manager Craig Counsell. Whatever Hader’s future role, let’s appreciate what the 24-year-old is doing in the here and now because it has been nothing short of spectacular.

Hader has improved upon his dominant 2017 rookie campaign en route to cementing himself as perhaps the top reliever in baseball. While the surface level stats (0.65 FIP, 19.29 K/9) pretty clearly illustrate his abilities, the underlying statistics paint an even brighter picture.

Hader boasts the 4th highest strike rate, 3rd lowest contact rate, and 4th best swinging strike rate in the major leagues this season. Essentially, Hader consistently fills up the strike zone but is as about as unhittable as any pitcher in baseball. The only other relievers who come close to rivaling these figures are Aroldis Chapman and Edwin Diaz. The difference is that while Chapman and Diaz are utilized strictly in one inning, save situations, Hader collects six or more outs per outing.

If there were ever any chinks in Hader’s armor, it was his tendency to become erratic with his command at times last season. However, he has cut his walk rate from 11.7% in 2017 to 7.3% this season, which is a minuscule amount when compared to his astronomical strikeout percentage.

Here is a look at the K-BB% leaders since the day Hader got called up to the big leagues.

Josh Hader 45%
Chad Green 43%
Dominic Leone 36%
Edwin Diaz 35%
Aroldis Chapman 35%

This table is factoring in last season when Hader did not possess quite the same command he has demonstrated so far this season. Hader has thrown 11.2 innings through 18 games this season, which means that he is on pace for roughly 105 innings this season (provided the Brewers don’t eventually move him into the rotation). If he maintained his 19.29 K/9, he would rack up over 200 strikeouts as a reliever.

I know, I know, its April 18th and everyone loves throwing out on pace stats despite knowing that regression is inevitable, and I admit that Hader’s case is no different. If we extrapolate his strikeout totals by using the midpoint between his 2017 and 2018 K/9 figures and keep his same projected innings total, that would still give Hader 171 strikeouts on the season. To put that into perspective, the single-season strikeout record for a pitcher who was used solely in a relief capacity is 166 by Mark Eichhorn. A feat he accomplished over 40 years ago. Put another way, Hader would have strikeouts as a reliever than any starter on thirteen different teams had in 2017 (White Sox, Tigers, Royals, Twins, Angels, A’s, Mariners, Rangers, Braves, Marlins, Reds, Rockies, Padres).

Not only is Hader generating an unprecedented number of swings-and-misses, he is also including weak contact when hitters are able to put the ball in play. Coming into play on Thursday, Hader has the 10th lowest exit velocity allowed amongst all left-handed pitchers and is 4th in xwOBA behind only Andrew Miller, A.J. Minter, and Sean Doolittle.

Without bombarding you with more statistics regarding just how good Hader has been thus far, let’s take a look at the evolving repertoire Hader has used to overwhelm his opponents in the early going.

First, Hader has always been reliant on his mid-to-upper 90s fastball, which has become one of the least hittable heaters in the game. Hitters inability to make contact with Hader’s fastball is best illustrated by comparing his opponents Z-Contact% to other unhittable relievers of the same ilk.

Lowest In-Zone Contact% – 2008 – 2017

Pitcher Year Z-Contact%
Aroldis Chapman 2014 63.2%
Aroldis Chapman 2015 67.1%
Kenley Jansen 2011 67.3%
Aroldis Chapman 2012 67.4%
Craig Kimbrel 2017 69.1%
Josh Hader 2017 / 2018 69.5%
Carter Capps 2015 70.3%
Craig Kimbrel 2012 70.3%
Ernesto Frieri 2012 70.6%
Koji Uehara 2012 71.7%

When Hader throws his fastball in the zone, it is one of the least hittable offerings in the game, but when we include the fastballs Hader throws out of the zone as well, Hader’s dominance with the pitch becomes even more apparent.

Most Unhittable Lefty Fastballs


Pitcher Fastball Contact%
Josh Hader Four-seam 62.1%
Justin Wilson Four-seam 66.1%
Andrew Heaney Two-seam 69.5%
Rich Hill Four-seam 69.5%
Sean Doolittle Four-seam 70.9%
Matt Strahm Four-seam 71.1%
Tony Cingrani Four-seam 71.9%
J.A. Happ Four-seam 72.4%
Scott Alexander Two-seam 72.6%
Chris Sale Four-seam 72.9%


Throughout his minor league career, Hader was able to generate a large number of swings-and-misses on his fastball simply by blowing it by hitters, but with a good, but not great average fastball velocity of 94.80, his effectiveness with his fastball goes far beyond merely reaching back and firing.

Hader also has demonstrated improved command with his fastball since debuting in 2017.

Compare the heatmaps of all the fastballs Hader through in 2017 versus the fastballs he has thrown this season:

Hader’s Fastball Locations in 2017:

Hader FB Heatmap 2017.png
Hader’s Fastball Locations in 2018:

Hader FB Heatmap.png
A year ago, Hader was able to get by with his fastball despite frequently locating the pitch in the middle of the zone, but as the above heatmaps show, he has made a deliberate effort to start attacking the corners with more frequency.

Even with better command on his fastball, he probably catches too much plate with many of his fastballs, which is why his effort to become less predictable in fastball counts has become so vital to his success.

Below is a chart comparing the counts in which Hader was most likely to throw a fastball in 2017 compared to how he deploys the pitch this season.

Josh Hader’s Fastball Usage By Count:

2017 2018
First Pitch 81.5% 63.4%
Even in Count 77.5% 66.7%
Pitcher Ahead in Count 76.9% 66.1%
Pitcher Behind in Count 93.8% 79.6%

Last season, Hader followed a fairly typical pattern when his fastball. Hitters could expect to get a heater on the first pitch and then again if Hader fell into an unfavorable count. This season, however, Hader has clearly departed from traditional pitch sequencing in order to keep the hitter off balance. No longer is Hader pouring in fastballs in the counts in which hitters expect them the most. Instead, he has bought into league-wide trend of pitching backward to hitters, which has so far looked to be a sound strategy.

Pitchers tend to throw their fastballs earlier in counts because it is the pitch that they have the most confidence in locating. The problem with this, however, is that hitters will often mistake these get-it-in fastballs because they are sitting on them. In fact, hitters have posted a .395 xwOBA on first pitch fastballs since 2015 when data such as this started to be collected. On first pitch sliders, this number drops to .354 and that is even mentioning that the contact rating on first pitch sliders compared to first pitch fastballs is over 10% lower.

The usual counterargument to pitching backward like this is that pitchers are not as effective at locating their breaking balls and so employing this strategy would force the pitcher to fall behind in counts more often. With Hader this is not the case. In fact, Hader’s first pitch strike percentage has improved from 58.5% to 61.5% so far this season.

Given these facts, it should come as no surprise that hitters are more helpless against Hader’s fastball than they were a year ago. Opponents wOBA against Hader’s fastball dropped from an already impressive .261 mark a year ago to just .170 this year. Hader’s fastball is already among the best in the game, but now that hitters can’t predict when it’s coming, it has become virtually unhittable.

Throwing fewer fastballs necessarily means that Hader has been utilizing his slider with more frequency. Instead of rearing back and throwing a fastball in counts that would historically call for one, Hader has opted to throw his slider instead. Similar to Hader’s fastball, his slider is absolutely deadly, even when hitters are expecting it. Just for fun, let’s enjoy watching Hader make opposing hitters look foolish with the pitch.

Josh Hader Slider GIFs.gif

So yeah, Hader’s slider is pretty nasty. Unfortunately for hitters both the velocity of the pitch and the frequency with which it is used has spiked since last season.

Below is a graph showing how Hader’s slider usage compares to a year ago.

Hader slider usage.png

Similar to the fastball, Hader has increasingly used his slider in typically fastball counts. Additionally, Hader’s location with the pitch has also improved since last season, as evidenced by the chart below.

Hader Slider Locations – 2017

Hader Slider Heatmap (2017).png

Hader Slider Locations 2018:

Hader Slider heatmap (2018).png
Hader has dramatically reduced the number of sliders he leaves up in the zone this season and has consistently pounded the zone low-and-away against left-handed batters. In essence, Hader has become less predictable in his pitch usage while also improving his location. While he was already probably one of the top relievers in baseball, these changes have not only made him better, but they also serve as signs that Hader continues to find ways to improve.

Perhaps the only flaw in Hader’s game is the development of his changeup, a pitch he throws less than 2% of the time. To be fair, Hader may see no reason to throw a third pitch when he has been able to dominate opposing hitters with his lethal two strike mix. Abandoning a pitch after being moved to the bullpen is typical for many pitchers who make this transition, so it could very well be the case that Hader isn’t throwing his changeup simply because he doesn’t need to. With that said, if he is ever going to occupy a spot in the Brewers rotation, developing a changeup will be essential when working through an opposing lineup for a second or third time.

Hader has always been one of the most talented lefties in the game and the deliberate changes that he has incorporated since his rookie campaign demonstrate that he is only going to get better.

While you can’t argue with the track record perennial All-Star closers like Craig Kimbrel, Kenley Jansen, and Aroldis Chapman, it is the lesser known Josh Hader who has arguably taken the throne as the best relief pitcher in baseball. Unlike the closers listed above, Hader frequently throws multiple innings and is employed by manager Craig Counsell in high leverage situations whereas the other players listed above are arbitrarily pigeonholed into the closer role, only toeing the mound when there is “a save situation”.

Last but not least, Josh Hader is under team control for six more seasons and because the MLB’s archaic arbitration system that inexplicably rewards relievers for saves above all else, Hader could conceivably remain cheap even through his arbitration years.

Yes, I just wrote probably upwards of one thousand words telling you what you may have already known — Josh Hader is very good. The point is not just that Hader is one of the premier bullpen arms in the game, the point is that despite Hader already dominating in historical fashion, he is showing us that this is just the beginning.


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