As absolutely everyone on earth knew they would, the Cubs went out and traded for a starting pitcher to reinforce their battered rotation. But somewhat surprisingly, they didn't end up with Sonny Gray or Chris Archer. Instead, they traded four prospects to the cross-town White Sox for Jose Quintana.
Quintana doesn't have the name value of Gray or Archer; as a Minor Leaguer, he was let go for nothing by both the Mets and the Yankees. He's also got an inflated 4.49 ERA this year, and suddenly you can hear Cubs fans wondering why the defending champs gave up two Top-100 prospects in Eloy Jimenez (No. 8, per MLBPipeline) and Dylan Cease (No. 63), plus two others, to get him.
So let's explain exactly that. No, Quintana isn't Max Scherzer or Chris Sale. Few are. What he is, is an above-average pitcher who brings two qualities the Cubs are short of in the rotation: durability and long-term control.
For all the surprising things that have gone wrong for the Cubs in 2017, issues in the rotation were pretty easy to see coming. We were talking about this last November when we suggested trading Kyle Schwarber (then at the peak of his value) for young, talented pitching, noting that Jacob Arrieta and John Lackey were to be free agents after 2017 and that at the time, "the Top 15 Cubs prospects at MLBPipeline.com [didn't have] a single pitcher who has spent a full season above Class A ball." Looking at the list now, only two of the Top 15 have made it to Double-A.

Quintana, meanwhile is under team control through 2020, with approximately $33 million remaining if all team options are exercised. That's not exactly a large sum of money these days; last offseason, Kendrys Morales and Brett Cecil (good players, hardly difference-makers) signed deals in that range. And if we compare Quintana, working on his fifth straight 200-inning season, to other notable pitchers over the past few years, you'll see how well he stacks up.
Over the past four years (since 2014)
Quintana: 719 IP, 3.47 ERA, 3.31 FIP
Archer: 731 IP, 3.60 ERA, 3.32 FIP
Over the past three years (since 2015)
Quintana: 518 2/3 IP, 3.52 ERA, 3.50 FIP
Johnny Cueto: 543 1/3 IP, 3.40 ERA, 3.54 FIP
Over the past two years (since 2016)
Quintana: 312 1/3 IP, 3.63 ERA, 3.71 FIP
Marcus Stroman: 316 1/3 IP, 3.98 ERA, 3.77 FIP
As we said, you wouldn't compare Quintana to, say, Clayton Kershaw. But he compares favorably to others who profile as strong No. 2s, and that's what the Cubs paid for. (Remember that when the White Sox dealt Sale last offseason, they got Yoan Moncada and Michael Kopech, and while Jimenez may be comparable to Moncada, Kopech is more highly regarded than Cease.)

But OK, that's previous years. What about right now? What about Quintana's 4.49 ERA? It's an extremely fair question to ask, because the Cubs are getting his future, not his past, and if there was evidence of diminished skills, then that would bode poorly for them.
That doesn't appear to be the case, however. Quintana's velocity isn't down; it's in the same 92 mph range it always is. What's mostly interesting is the word "more," both good and bad. More strikeouts. More walks. More homers.
Let's start with the whiffs, because between 2014-16, Quintana was basically league average, strikeout-wise. He struck out 21.2 percent of hitters he faced, comparable to Julio Teheran (21.1) or Scott Kazmir (21.3), and near the Major League average of 20.9. But this year, that's up to 24.6 percent, which is not only above average, it's better than Jonathan Lester (24.1) or Arrieta (23.5). Of course, Quintana's walks are up, too (9 percent, up from his usual 6.5), and so are the homers (1.21/9, up from last year's 0.95), though it's difficult to isolate if that's his change or just that everyone's allowing more homers.
With some new Statcast™ metrics, we can dig a little deeper to see if there's underlying changes in Quintana's skills. By looking at the league outcomes of every combination of exit velocity and launch angle, we can strip out the effects of defense, positive or negative, and simply credit a pitcher on the quality of contact skill they just exhibited. We express this as Expected wOBA, where wOBA is just like OBP other than that it allocates more credit to extra base hits rather than treating each time equally.
The Major League average for expected wOBA this year is .315. In 2015, when Quintana had a 3.36 ERA, he had a .307 xwOBA, so just above average. Last year, with a similar 3.20 ERA, he managed to cut that down to a very good .293 xwOBA, 29th-best among starters, and tied with Arrieta. This year? Despite that 4.49 ERA, that xwOBA is .300, exactly his average since 2015, and 35th among starters, just behind Robbie Ray.

Those rankings sound right, by the way. If we say there's approximately 20 true "aces" in the game, then Quintana is right in the middle of a strong second tier. So where's that 4.49 ERA coming from? While you can't simply cherry-pick good starts, it's worth noting that Quintana had back-to-back disaster starts, allowing eight earned runs to Arizona on May 24, then seven against the Red Sox on May 30. Aside from those two starts, his ERA is 3.54; his career ERA is 3.51. And since that Boston start, Quintana has allowed 12 earned in 40 innings (a 2.70 ERA), notably striking out 10 Rockies in 5 1/3 innings in Coors Field last week.
The point is that while that 4.49 ERA certainly doesn't look great, the more you look under the hood, this more this looks like the same Quintana we've seen every year, and he's about to find things just a little easier. While the Cubs defense has had their issues trying to repeat last year's historic run, they're collectively a +23 DRS, compared to the -4 of the White Sox. And don't forget: Quintana leaves the land of the designated hitter, where the American League has collectively hit .256/.325/.427 (.322 wOBA), to a National League (254/.323/.424, .319 wOBA) where he can face pitchers every nine batters.
The Cubs, it must be said, needed to do something to reinforce the rotation now, while they still have a chance to run down the Brewers, and for the future, given the likely departures of Arrieta and Lackey. It didn't come cheaply, because good pitching never does. But this is about the going rate for a good No. 2, and both sides have to walk away pleased.