The Astros, one of baseball's most famously analytical teams, managed to pull off a pretty interesting math trick over the past eight months. They identified approximately 365 pretty poor innings that were thrown for them last year, and they got rid of them, mostly. In their place, they've replaced them with approximately 365 new innings from a pair of possibly elite-level pitchers who weren't with the team one year ago. Not a bad trade for a team that had already just won the World Series, right?
The end result? One of last year's better pitching staffs might be even better than you thought it was going to be this year -- and we already thought it was going to be really, really good.
The Astros entered Wednesday with a 2.02 ERA, by far the best in baseball. They have a 2.56 FIP, the best in baseball, and a .292 Expected wOBA, the fourth-best in baseball. They have the second-highest strikeout rate (29.1 percent) and the sixth-lowest walk rate (8.1 percent). The supposedly great offense hasn't even been that good (merely middle of the pack), yet the 9-3 Astros are tied for the most wins in the Major Leagues. The pitching has been that good.
That won't all last, but obviously this is going to be one of the best staffs in baseball. There's a few reasons for their success; let's start with the simplest: The improved talent level of the pitchers receiving a big chunk of their innings.

Last year, the quartet of pitchers below combined for 365 innings of 5.23 ERA. Three of the four are no longer with the organization, and the fourth is back in the Minor Leagues.
These four 2017 pitchers are gone
Mike Fiers, 5.22 ERA, 153 1/3 innings (free agent, Tigers)
Joe Musgrove, 4.77 ERA, 109 1/3 innings (traded to Pirates)
Michael Feliz, 5.63 ERA, 48 innings (traded to Pirates)
Francis Martes, 5.80 ERA, 54 1/3 innings (now in Triple-A)
Not great -- though you will be able to win trivia competitions for the rest of time by knowing that it was actually Fiers who threw the most innings for the 2017 World Series champs. You likely already know who the Astros have in their place, but let's remind you. This is … better. They cut from the bottom and added to the top.
They have been replaced in 2018 by
Justin Verlander, 1.45 ERA in 18 2/3 innings so far
Gerrit Cole, 0.64 ERA in 14 innings so far
Verlander already threw 34 of his 206 innings for Houston last year, so another 200-inning season would be 172 "new" innings. Cole threw 208 and 203 innings in his past two healthy seasons for Pittsburgh, in 2015 and '17. If he contributes another 200, there's your 370 or so innings, an almost-perfect replacement. Those two won't continue to pair for a 1.10 ERA all year long, of course, but they don't have to in order to beat the contributions Houston got from Fiers, Musgrove, Feliz and Martes last year.
So it's a little about simply having better talent. It's a lot about the way the Astros use that talent, too.
Last year, there was no better exemplification of that than in Charlie Morton, who for a decade had been an oft-injured, occasionally productive back-end starter. Despite having made only four starts for the 2016 Phillies, the Astros saw Morton's increased velocity and high-spin curve, encouraging him to use the latter more often. He ended up closing out Game 7 of the World Series.
In 2018, that's Cole, in perhaps the most obvious example of "an absolutely perfect fit between player and team." For all of Cole's clear talent, he was more good than great last year with Pittsburgh. That's in part because while he had elite fastball velocity (95.9 mph, seventh among starters), it had average-to-slightly-below spin rate, which is to say that it was a straight pitch that didn't move much -- reflected in the fact that Cole had merely a league-average strikeout rate for his career.
Last year, the Pirates threw more fastballs than any other team in baseball. The Astros, conscious of the growing trend away from fastballs in baseball, threw the sixth fewest. When we looked at a few pitchers this spring who might benefit from fewer fastballs and more breaking pitches, Cole was high on our list. Guess what happened? The sinker, which allowed a .515 slugging percentage last year, has all but disappeared. There are more curves and sliders, along with the high-velocity four-seamer.

Cole has made 129 career starts, including two this season. He managed to get 21 swinging strikes in his first start and 20 in his second. They're the two highest numbers of Cole's career. This is not a coincidence.
Nor was it for Verlander, who has now thrown 52 2/3 innings across eight regular-season starts for Houston -- and allowed seven earned runs. While much was made of a report that the Astros had helped improve his slider last summer, what they've really done is accelerate a long-running trend. Verlander is now throwing that slider a career-high 27.2 percent of the time, with his recently ineffective changeup all but gone.

What this all means -- adding talented pitchers to a staff that already had Dallas Keuchel, Brad Peacock, Lance McCullers, Chris Devenski and more, and helping them throw better pitches more often and more effectively -- is that the Astros rank highly in some extremely interesting categories right now.
They get the third-most swings on pitches outside the zone, and in case you're wondering if that's important, the top two teams are the Yankees and Indians. On those swings, Houston is allowing the second-lowest contact, just 55.7 percent. The club throws the seventh-fewest fastballs but throws them at the third-hardest velocity, while throwing the third-most curveballs to go with them.
None of that means the Astros will keep up the 2.02 ERA, because they won't. Yet Houston was already great last year, and then the team added Cole, Hector Rondon, Joe Smith and a full season of Verlander. They're so deep that Peacock, a top-three starter on most teams, can't crack the rotation. Longtime starter Collin McHugh, who made 102 starts for the team between 2014-17, is now working out of the bullpen, and has seen his fastball velocity jump from 90.3 mph to 91.8 this year. He's struck out 10 in his first 6 2/3 innings, with a 1.35 ERA.
In the Minors, James Hoyt, who struck out 66 in 49 1/3 innings last year, is rehabbing in Triple-A and may need to stay there. The Astros will also likely have Forrest Whitley, the No. 9 prospect in baseball, available later this season when he returns from suspension. Martes remains highly regarded and is only 22 years old. There's more talent than they can fit on the roster.
A good way to ratchet up the hyperbole is to realize that the 2017 Indians had a decent argument for "best pitching staff ever," as wild as that is to believe. As great as Corey Kluber and Andrew Miller are, it's difficult to look at the names on that roster compared to this one and see a significant difference in talent level. This Astros group won't just be good. It's going to be great. It already is.