Edwin Diaz was recently named the American League Reliever of the Month. This is, evidently, an award that exists, and Diaz this year has already won it four times. The baseball season has had just five months. Diaz has been absolutely overwhelming, and no player is more responsible for having kept the Mariners competitive. Diaz’s Oakland equivalent would be Blake Treinen, who’s had a similarly impossible year. In the National League, there has, of course, been Josh Hader. You know who many of the best relievers are right now. You might’ve read a few articles about them over the course of the regular season. It’s along season, and almost everything gets written about eventually.

But there’s a reliever breakout that’s been happening under the radar. Over time, the 2018 Texas Rangers have faded from relevance. Yet, over time, those same Rangers have watched Jose Leclerc develop into something sensational. Leclerc maybe hasn’t been the best reliever in baseball. He’s definitely been one of them, however, and what makes it all the more remarkable is where Leclerc was just a season ago. Wild hard-throwers come, and wild hard-throwers go. Usually, they never manage to harness their stuff. Leclerc’s an exception who flipped a switch, and now the batters just don’t know what to do.

When Leclerc showed up as a rookie in 2016, he had a mid-90s fastball, and this weird sort of cut-changeup. The stuff was interesting, yet Leclerc wound up with a walk rate of 20%. No matter — it was only 15 innings. Could’ve been nerves. Leclerc came back the next year, but, once again, he wound up with a walk rate of 20%. He was hard to square up, that much was certain, but a 20% walk rate is almost literally unbelievable. It was one of the very highest walk rates in all of baseball history. Among pitchers with at least 40 innings in a season, it was the highest walk rate baseball had seen since 2003. Leclerc would sometimes struggle to throw even half of his pitches for strikes. That’s no way to earn a manager’s trust. That’s no way to extend a big-league career.

Following the 2017 regular season, Leclerc played some winter ball in the Dominican. Over 13 innings, he racked up 11 walks and 15 strikeouts. More of the same, more or less. Now fast-forward. Today is September 5. Seems like a good day to look at a table.

Leclerc has cut his walk rate in half. And, for every walk he’s subtracted, he’s added a strikeout. Even last season, Leclerc finished with one of the lower rates of contact allowed. That rate now is just as impressive. What’s changed is that Leclerc has just thrown more strikes. Put it all together and this plot should give you an appropriate picture. On the y-axis, you see expected wOBA allowed, for pitchers. On the x-axis, you see actual wOBA allowed. Leclerc’s is the point in yellow. You know how these work by now.

Few pitchers have allowed a lower wOBA. No pitchers have allowed a lower expected wOBA. And this gets into something fun and unusual. Of course, as far as wOBA is concerned, it’s important to generate strikeouts while limiting walks. But what’s the other component? That would be contact allowed. Leclerc is a fly-ball pitcher, but, more specifically, he’s an *infield*-fly-ball pitcher. Of Leclerc’s fly balls in 2018, 30% have been marked down as infield flies, according to Baseball Info Solutions. That would stand as the highest rate on record for pitcher-seasons of at least 50 innings. We have such information going back to 2002. The pitcher with the second-highest rate would be one Mariano Rivera.

Even last year, Leclerc finished with a high rate of pop-ups. Since 2002, 1,342 pitchers have thrown at least 100 career innings. Only one pitcher has a higher rate than Leclerc of infield flies per fly ball. And, let’s say you don’t necessarily feel comfortable with somewhat arbitrary designations from Baseball Info Solutions. We can turn to Statcast. This year, when Leclerc has allowed a batted ball, 30% of them have been hit with a launch angle of at least 45 degrees, which is around where batted balls become too high and harmless. The next-highest rate is lower, by multiple percentage points. Leclerc manages contact by getting hitters to hit the ball straight up. At this point, it has to be regarded as a skill of his.

As I write this, Leclerc has an actual strikeout rate of 39%. But a pop-up is also basically an automatic out, so if you fold those in, then he has an effective strikeout rate of 46%. Almost half the time, the batter has been an automatic out. And wouldn’t you know it, but over the course of the year, Leclerc has been improving.

In April and May, Leclerc had a K-BB% of 14%. In June, it was 30%. In July, 33%. In August and September, 46%. Since the start of July, Leclerc has thrown two-thirds of his pitches for strikes, which is not an unprecedented rate, but which *is* an amazing rate for Leclerc, given his own big-league background. It’s not like he figured something out during the offseason. He’s figured something out on the fly, and while his mechanics look pretty similar to my eye, there’s no denying that something must be going on. Maybe it’s confidence. Maybe it’s something else. The Leclerc of today has fastball command. Or, at least, he has fastball control. And that’s helped his cut-changeup, which he’s leaned on more heavily. As Leclerc has thrown more strikes, he’s made his best secondary pitch more dangerous, such that his cut-changeup has baseball’s second-lowest contact rate for any individual pitch thrown somewhat regularly. This is what it means, in a sense, to establish the fastball. When hitters know a pitcher can throw a strike with a fastball, it makes them more likely to swing over something else, out of the zone.

Just Tuesday, Leclerc had a pretty representative outing, nailing down a save in 1-2-3 fashion. Here’s the Rangers’ new closer starting things off with a cut-change for a called strikeout:

That was followed by a cut-change for a swinging strikeout:

And that was followed by a fastball that got popped sky high:

This is what the Rangers are growing accustomed to. Leclerc last allowed a hit on August 16. He last allowed a run on July 25. In that outing, he allowed a home run, which still stands as the only home run he’s given up. While Leclerc has been used almost strictly as a one-inning reliever, he’s generated multiple strikeouts in nine of his last ten appearances. When the season began, the Rangers would’ve been right to assume that Jose Leclerc would again resemble Jose Leclerc. A hard-throwing righty with far too much trouble staying in the strike zone. What the Rangers have now is someone who’s both overpowering and overwhelming. For the Rangers, this hasn’t exactly been the most encouraging season in terms of pitcher development, but you can count that as yet another way in which Leclerc stands out from the pack.

The pitcher who couldn’t throw strikes figured out how to throw strikes. Pitchers like this will forever get ample opportunities, because evaluators can’t help but dream on their ceilings. Most of those pitchers remain ineffective. Every so often, you get a Jose Leclerc. There’s no one else out there getting the job done in quite the same way.