The Astros just finished a season during which their pitching staff was legitimately one of the most dominant groups we've seen in decades, and a large portion of the credit for that success lies with their starting rotation. Their five primary starters combined to make 152 of the team's 162 starts, and they were one of only three teams to have five pitchers make at least 22 starts.
Pretty good, right? Well, let's take a look at how that quintet stands headed into the offseason.
Justin Verlander -- turns 36 in February, free agent after 2019
Gerrit Cole -- free agent after 2019
Lance McCullers -- out for 2019 after Tommy John surgery on Tuesday
Dallas Keuchel -- currently a free agent
Charlie Morton -- currently a free agent
Needless to say, there are some holes to fill next season and beyond. We won't be seeing the same group that pushed Houston to 103 wins in 2018.
It's hardly a dire situation, of course. The Astros could simply move relievers Collin McHugh and/or Brad Peacock back to the rotation, where each have experience, a move McHugh seems eager to make. Flame-throwing Josh James, who started three times, could get a look. Top prospect Forrest Whitley, currently the No. 8 overall prospect, according to MLB Pipeline, almost certainly will receive some 2019 starts. So might Cionel Perez, Framber Valdez or Corbin Martin. The Astros are rich in talent.

But there's something else going on in Houston that's important. As we examined last month, its emphasis on analytics and technology seems to have made it the industry leader in taking talented-but-underperforming pitchers and making them better. That's Verlander, Morton and Cole; it's also Ryan Pressly and Will Harris, and assuredly others.
It's to the point that the Astros seem to have something of a reputation as a place you go if you want to improve, at least if you're willing to buy in. Pressly told the Washington Post as much, saying, "It's the preparation of the [Astros'] analytics department. They tell us what works and what's not going to work." He went from being a good reliever with the Twins to a dominating one with the Astros.
Every team works with data to varying extents, but the Astros -- from pitching coach Brent Strom on down -- seem as if they're doing a better job than anyone getting that information onto the field in a way that players can truly benefit from it.
With that in mind: Who's next? The Astros obviously have a need for a starter or two, and while it remains possible that Morton or Keuchel return, it's more interesting to imagine the next half-decent arm who comes to Houston and blossoms into a star. Often in Houston -- though not always -- it's about identifying spin, and using it properly. Verlander, Morton, Pressly, Cole and McHugh all rate as high-spin outliers, and the Astros as a team were first in four-seam spin and first in curveball spin, by a lot. Like velocity, spin doesn't by itself make you successful, but the Astros seem to do a great job in harnessing it.
We're not talking about the bigger names on the market like Patrick Corbin or Nathan Eovaldi. Let's find some pitchers who haven't sustained success, who might find themselves breaking through in Houston. Their recent track records may raise some eyebrows, but that's the point -- and remember, so did Morton's when the Astros signed him after the 2016 season, during which he made just four starts in Philadelphia.
Sonny Gray, Yankees
Gray isn't a free agent, but the Yankees have made it perfectly clear they're going to trade him, so he fits here. We investigated Gray's troubles earlier this week, and came away unconvinced anything was more seriously wrong than an aversion to pitching in Yankee Stadium. (Gray had a 6.55 ERA at home in parts of two seasons as a Yankee, but a sparkling 2.84 on the road.)
That means plenty of teams would be interested, but we know the Astros already tried to get Gray in 2017, and he's got 90th percentile spin on both his fastball and his curveball. Of the 11 names ahead of him on the curveball spin list, three (Pressly, Morton and Verlander) were Astros in 2018. If anyone can unlock Gray, it might be Houston.

Trevor Cahill, free agent
One of the other names higher than Gray on the curveball spin list is Cahill, who has cycled through the D-backs, Cubs, Padres, Royals and A's since 2014. Thanks to a variety of injuries to his knee, shoulder, elbow, Achilles and back, he hasn't topped 110 innings in a season since 2013.
You could have said something similar about Morton. But when healthy, Cahill was quietly effective for Oakland this year, as he was early in 2017, and he threw that high-spin curve only 16 percent of the time, allowing just a .145 average and a .261 slugging percentage on it. He was also one of only five pitchers to get a 50 percent grounder rate and a 20 percent strikeout rate, along with McCullers, Gray, Aaron Nola and Walker Buehler.
Garrett Richards, injured free agent 
Richards underwent Tommy John surgery over the summer and won't pitch until 2020, so this would be more of a long-term play -- just like when the Rays signed an injured Eovaldi in '17, looking ahead to what he might offer in '18. (The answer: 57 good innings and a solid pitching prospect in Jalen Beeks, from Boston.)
Richards has had repeated injury problems, first to his knee and then his arm, so he made only 28 starts over the past three seasons, and he won't be adding to that in 2019. They've always been high-quality innings, though -- a 3.15 ERA in 514 2/3 frames since '14 -- and he was probably the first notable high-spin-rate pitcher unearthed by Statcast™ when the system came online in '15.
Of all starters with 1,000 fastballs thrown since 2015, Richards is second only to Verlander in spin, and he's No. 1 in curveball spin among starters with 250 thrown. He wouldn't help in 2019, but Houston needs arms in '20 and beyond, too.

Thomas Pomeranz, free agent
Pomeranz has been consistently inconsistent: an All-Star with San Diego in 2016, 173 2/3 high-quality innings with Boston in '17, an injury-plagued and ineffective '18, and a somewhat stunning placement on the Red Sox's World Series roster. He's also been a high-spin fastball type, and at his best, his curveball has been an effective weapon. It wasn't Pomeranz's best, or near it, in 2018, allowing a .380 average and a .529 slugging this past season.

Jeremy Hellickson, free agent
If you're sensing a pattern here, it's "veteran with high spin rate who has been unable to stay both productive or healthy," which is basically the Morton profile, and that brings us to Hellickson, who has been on five teams in the past five seasons. In that time, he's been durable (121 starts), but only moderately productive (4.39 ERA), and with a below-average 18 percent strikeout rate.
So what's of interest here? It seems like Hellickson was auditioning for the Astros last year, all but abandoning his sinker (down to three percent) while upping his curveball usage (23 percent, up from 12 percent). He's also in the Top 10 of that "starter curve spin since 2015" list, but the pitch has been more good than great. 
Others: Tyson Ross, free agent (elite fastball spin, but declining velocity); Aaron Sanchez, Blue Jays (elite curveball spin, but health issues and uncertain availability); Dylan Bundy, Orioles (elite fastball spin, but home run problems and uncertain availability). 
Bonus trade target: Tyler Chatwood, Cubs 
We said many of the same things last December about Chatwood, even suggesting he could be the "next Morton." He wasn't. Chatwood signed a three-year deal with the Cubs, then walked more (95) than he struck out (85), and the Cubs simply stopped using him in the midst of a tight National League Central race -- he pitched just once after Aug. 18.
Chatwood might be a lost cause, but the underlying skills that attracted the Cubs to him are still there. He's available for nothing more than money, likely less than his full contract, since Chicago would probably pay down some of it, and who better than the Astros to try to turn him around?