Randall Delgado is pitching great — or is it just his catchers?

Offense isn’t the only thing fueling the Diamondbacks’ surprising start this year. For the first time in a long time — since 2012, to be exact — Arizona has a pitching staff that’s above-average in both ERA and FIP. And they haven’t been middle-of-the-pack, either: Only the Dodgers have more fWAR (13.0) and RA9-WAR (15.0).

The big names have played a role in that — Zack Greinke has dominated like the Diamondbacks expected he would when they gave him $205 million, and Robbie Ray is pitching up to his talent. New guys such as Zack Godley have broken out to help the team even more. But one of the bigger, more unsung successes is an Arizona stalwart who appears to have put everything together: Randall Delgado.

Paul Goldschmidt has reached a new level

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The Diamondbacks’ underappreciated star is raising the already lofty bar he’s set for himself.

A consensus top-100 prospect as a starter with the Braves, Delgado came to the desert before the 2013 season in the Justin Upton trade. Over his first four years with the Diamondbacks, he had some ups (a 3.25 ERA in 2015, a 3.39 FIP in 2014) and some downs (a 4.87 ERA in 2014, a 4.99 FIP in 2013). Overall, he was a thoroughly pedestrian pitcher, whose 4.22 ERA and 4.21 FIP in 341 innings helped the team yet didn’t stand out.

2017 has seen Delgado turn a corner. Across 57 ²⁄₃ frames — with five starts and 18 relief appearances — he’s notched a 3.28 ERA and 3.21 FIP. Those are impressive enough on their own; when you take into account the leaguewide trend toward more scoring, they’re the best marks of his career. In his fifth year with Arizona, the 27-year-old righty has looked like the guy prospect evaluators thought he could be.

Looking at Delgado’s Pitch Info plate discipline data on FanGraphs reveals an interesting trend. Delgado isn’t throwing the ball in the strike zone more than he used to, or getting hitters to chase more often. Instead, a lot more calls have gone his way:

Back in 2013, Delgado pounded the strike zone at the expense of his whiff rate, which was 9.7 percent that year. When he moved away from the zone in 2014 and 2015, he saw his swinging-strike rate spike to 14.1 percent. Last year those whiffs abandoned him, but this season they’ve returned — he’s gotten hitters to swing-and-miss at 12.9 percent of his pitches. And since he’s paired that with more strikes overall, that gives us this graph:

Image via FanGraphs

Delgado’s 23.0 percent strikeout rate in 2017 isn’t a career best — he fanned 24.6 percent of the batters he faced during 2014 and 2015. Nor is his 5.0 percent walk rate a new low, as he issued free passes 4.9 percent of the time back in 2013. But by combining the two, Delgado has excelled like never before. Simple!

Figuring out who deserves the credit for Delgado’s turnaround is a little bit trickier. After several years of Welington Castillo and his ilk behind the plate, the Diamondbacks finally brought in a couple of solid framers this year — Jeff Mathis and Chris Iannetta, who have caught 55 ²⁄₃ of Delgado’s 57 ²⁄₃ innings in 2017. Those catchers rank seventh and 11th in the majors, respectively, in Called Strikes Above Average.

Delgado hasn’t thrown the ball to the edge of the strike zone any more than he used to, yet Mathis and Iannetta have gotten him more strikes (just as they have for Greinke). Does this mean he hasn’t really improved — that the scenery around him has made him look like a top-flight pitcher when he remains the same pedestrian swingman he was last year?

Not so fast. Mathis and Iannetta aren’t the only factors at play here; Delgado has made significant progress in a few other regards. This is the first year since 2013 that Delgado has spent consistent time in the rotation — from 2014 to 2016, he started five games, a total he’s already matched this season — and as he told AZ Central’s Nick Piecoro, he’s come a long way since then:

Delgado throws essentially the same mix of pitches he did back then, but he thinks he’s gotten better at repeating his delivery.

“Even if the movement is the same as before, my location is better,” Delgado said, “and I think that’s the more important thing.”

This is a pretty noticeable trend, especially with Delgado’s fastball mix. He throws a four-seamer as his bread-and-butter pitch, with a sinker to back it up, and those pitches have gone in opposite directions this year:

Image via Brooks Baseball

What happens when you throw one pitch high and the other pitch low? Delgado’s four-seamer has seen its whiff rate increase to 10.7 percent this year, while his sinker’s ground ball rate has spiked to 53.6 percent. Overall, Delgado’s 45.8 percent ground ball rate is the highest of his Diamondbacks career, and as noted earlier, he’s managed to recover some of the swinging strikes he lost last year. Without these changes in location, none of that could have happened.

And then there’s the secondary pitches — a changeup and a slider, which Delgado has swapped this year:

Image via Brooks Baseball

While these pitches are pretty similar in terms of swinging strikes, the changeup has always had a much higher strike rate (66.9 percent) than the slider (55.5 percent). Mathis and Iannetta have had a much easier time bringing the cambio into the strike zone. Better fastball location, along with a move from breaking balls to offspeed pitches, has given Delgado better results across the board.

Like so many of his Arizona teammates, Delgado has reached a new echelon this year. And as is the case with many of them — and with many baseball achievements in general — multiple parties deserve recognition for making this happen. Iannetta and Mathis have done what the Diamondbacks brought them in to do; Delgado, in turn, has tweaked his approach and taken off.

Ryan Romano is the co-managing editor for Beyond the Box Score. He also writes about the Orioles for Camden Depot, sometimes. Follow him on Twitter if you enjoy angry tweets about Maryland sports.