Last year’s Brewers were a surprise contender, hanging around the race until the end of the season. It’s always a good thing when a team arrives ahead of schedule, but it can force a rebuilding organization to strike a new balance of short-term vs. long-term considerations. One decision the Brewers made was to call up pitching prospect Josh Hader so as to use him out of the bullpen. Hader was a starter with promising stuff, but the Brewers wanted later-inning reinforcements. To Hader’s credit, he thrived in his new role, starring down the stretch as a fireman.

It can get tricky when starters pitch in relief. Fans often worry that a prospect might end up stuck in the bullpen, accumulating fewer innings. Throughout the offseason and into the spring, there were questions regarding Hader’s present and future. Would the Brewers stretch him back out, or had Hader found his place? We’ve all grown up thinking of starters as being more valuable than relievers. Yet, in this age, starters are throwing fewer innings than ever. And as for Hader specifically — well, the matter isn’t so tricky when you’re talking about maybe the most valuable reliever around. Josh Hader was already good. Now he’s simply sensational.

The best Brewers bullpen, of course, would include a healthy Corey Knebel. He’s another critical 2017 breakout. But let’s just focus on Hader here. Hader, so far, has made six appearances, throwing 9.2 innings. Here are his game-by-game walks:

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Meanwhile, here are his game-by-game strikeouts:

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Hader has faced 34 batters. He’s struck out 22 of them, while allowing only two hits. He’s making high-leverage appearances, and in five of six games, he’s recorded more than three outs. A start like this would be worth noticing on its own, but this comes on the heels of Hader figuring out strikes in the middle of last August. Hader hasn’t been dominant for only six games. It looks like he’s recently gotten more dominant, but he was already fantastic before. This is more than only a start.

What Hader brought into the season was an unhittable fastball. Hader’s fastball racked up swings and misses down the stretch last season, even though Hader leaned on it heavily. It’s telling when a majority pitch still gives hitters fits, and here’s a recent, fairly representative swing. The fastball is still there.

While Hader has good velocity, it’s not elite, especially among relievers. And I wouldn’t say his fastball comes with an awful lot of rise. If I had to guess, I’d say that Hader benefits from a highly deceptive delivery. You can tell from that clip that he’s cross-fire to the plate, like a left-handed Jake Arrieta. Here are average 2018 pitcher release points, with Hader being the data point in yellow.

Hader has funk, and his fastball should be considered to be a proven weapon. Based on that, Hader was already outstanding, but now we’re starting to see something new, as well. With ever-increasing confidence, Hader is using his slider.

It’s a slider that can make even Kris Bryant look like a high-school freshman seeing a curveball.

Hader threw a slider last year as a rookie. He just didn’t throw it all that much, going with more fastballs and the occasional changeup. Hader’s slider now breaks similarly, but it’s picked up by a tick or two. And this hasn’t been only a two-strike putaway. Across all situations, Hader is putting his second pitch to use.

There are no more obvious fastball counts. Not that those were ever easy to begin with, given how good Hader’s fastball is, but a pitcher can never have too many advantages. And Hader has found that he prefers his slider to his changeup, even against right-handed bats. Why might Hader feel so much better about his slider, all of a sudden? That’s revealed by where his sliders have gone. His location seems to be dramatically better.

I know I’ve been coming at you with image after image. I don’t mean to be overwhelming. The general point is this: Hader arrived in the majors having had trouble throwing strikes in Triple-A. Right in the middle of last August, Hader got himself under control, and he thrived while leaning heavily on a hard-to-hit fastball. His current fastball is no more hittable than it was, but, now, Hader also has a second pitch he considers reliable. A dominant, multi-inning reliever effectively added a pitch. Going back to the middle of last August, then, here are major-league relievers, by contact rate and strike rate. Hader is in yellow again.

Out of a pool of 184 relievers, Hader has had the fourth-highest strike rate, and the third-lowest contact rate. The most similar relievers in these two regards are Edwin Diaz and Aroldis Chapman. Diaz and Chapman are closers, but they’re also mostly one-inning relievers, while Hader is far more flexible. And just to go with one more selection of results, here are the top K-BB% marks for relievers since the middle of August, setting a minimum of 75 batters faced. Hader, for the record, has faced 116.

Hader has only one save to his name, and, like it or not, we still tend to give extra credit to closers. And since a lot of relievers have this nasty habit of being unpredictable, you might prefer to look to the long-standing track records. When you think of the most valuable relievers around, you might think of Chapman, or Kenley Jansen, or Andrew Miller. But not only has Hader been maybe the best per-inning pitcher in the game — he costs about the minimum, and he has six years of club control. Chapman’s expensive. Jansen’s expensive. Miller’s in his contract year. When you fold in the contract situation, too, alongside the performance, Hader could very well be the most valuable reliever. Green is right there. He has five remaining years of control, but that’s less important for pitchers than it is for position players. Pitchers should mostly be considered valuable in the short-term, and unknowable further out. So Hader’s service time matters, but he’s not exactly Ronald Acuna.

If Josh Hader isn’t baseball’s most valuable reliever, he’s close. He could get there soon, elbow willing. Plain and simple, he does everything right, going multiple innings at a time and pitching well independent of batter handedness. You could think of him as peak Dellin Betances, another non-closer who racked up strikeouts over 70 or 80 or 90 innings. Betances made four consecutive All-Star Games. Maybe his control is starting to go, but nothing is forever. Hader is that good, and he’s only improved since basically doubling the size of his repertoire.

Maybe Hader would be more valuable still as a starter. I honestly couldn’t tell you. Neither could the Brewers. Perhaps they haven’t closed the door on that possibility. But, what Josh Hader is today — he’s not a pitcher who needs to be changed. He gives the Brewers a massive advantage from exactly where he is.