First, take FIP, or fielding-independent pitching — i.e., what a pitcher’s ERA would probably look like with league-average defensive support and neutral luck. Last season, Verlander as you saw above put up an ERA of 2.58, but his FIP of 3.30 suggests he was a bit fortunate to have such a low mark. To be sure, 3.30 is quite strong, but it constitutes a decline from his 2018 FIP of 2.81. In related matters, Verlander last season benefited from a low batting average on balls in play (BABIP) of .219. Pitchers generally exhibit little control over BABIP, and most will settle in at somewhere between .290 and .300. When you see a single-season result like Verlander’s mark of .219 last year, it’s a good bet to find its way closer to career norms in the following season (Verlander’s pre-2019 career BABIP was .286). That increased BABIP will take his ERA along for the ride.
First, there’s no assailing the brilliance of Verlander’s award-winning work in 2019:  More concerning are Verlander’s velocity trends. Verlander first suffered velo loss from 2013-15, and at the time we were all wondering whether premature decline had set in. However, once Verlander got clear of the core, shoulder, and triceps problems that plagued him during those years, his arm got livelier. He began gaining steam in 2016, and by the time he was traded to Houston in late August of 2017 he was flashing something close to vintage heat. Look at the trends since then: 
At age 37, sudden decline is a genuine threat even if there’s no underlying sign of it in the statistical record. Verlander, though, has a handful of red flags — or at least fuchsia ones — that raise the odds of decline in 2020. Throw in his 35 1/3 subpar innings in the 2019 postseason (4.33 ERA and 5.20 FIP over that span) and the lat injury and groin surgery that limited him this spring, and you have some additional reasons for worry. 
Houston ace, reigning AL Cy Young winner, and future Hall of Famer Justin Verlander turned 37 years of age in February. Despite the fact that he’s coming off a dominant 2019 campaign, there’s some cause for concern beneath the surface-level numbers, and that raises concerns that Verlander will finally be entering his decline phase. That decline could some as soon as 2020, and the Astros may not be equipped to withstand it. 

Season Verlander’s average fastball velocity
2019 2017
The overarching concern for Houston is that they perhaps need Verlander to be his 2019 self for another year. Yes, they’ll have Zack Greinke as his No. 2 man for a full season, but Greinke himself is now 36. Since last season, the Astros have also bid adieu to Gerrit Cole, Wade Miley, Collin McHugh and Aaron Sanchez. Yes, Lance McCullers Jr. returns from Tommy John surgery, but he’s yet to work more than 128 1/3 innings in a major-league season. At the back end, they’ll be relying on Jose Urquidy and Josh James. They’re both promising, but the Astros of recent years have had some difficulties in getting top pitching prospects to transition successfully to the highest level.  94.8 mph
Additionally, Verlander led the majors in WHIP and paced the AL in K/BB ratio. He dominated at multiple levels — volume (that innings total led the majors), run prevention and K/BB ratio — and he was an eminently worthy choice for those Cy Young laurels. Moving forward, though, it’s not hard to find cause for concern, and moving forward is what matters for Verlander and the Astros.  95.8 mph

It’s not stark, but it’s another example of underlying decline. Suffice it to say, the recipe for surviving velocity loss is to improve command in the face of waning radar gun readings, but Verlander did the opposite last season. 
That’s not a huge difference, but it’s a trend in the wrong direction. His 2019 numbers also aren’t the result of a late-season dip, as he fastball averaged less than 95 mph in every full month of the season. What’s also worrisome is that Verlander last season saw his spin rate decline on fastballs and sliders. He remains near the top of the scale in terms of spin, but it’s another trend in the wrong direction. 

  • Verlander in 2018 had a CSAA of 0.46 percent. 
  • Verlander in 2019 had a CSAA of 0.15 percent.

If Verlander declines significantly, than the Houston rotation could be in trouble this season. To repeat the whole point of all this, yes, there’s a real risk of that. It’s too much to say the AL or even the AL West hinges upon Verlander’s ability to remain at peak level, but if age does start to have its way with Verlander in 2020 then consider it good news for the remainder of the junior circuit. 
Last season, Verlander in his age-36 campaign authored a Wins Above Replacement (WAR) of 7.4. His 2019 is one of just 21 seasons in which a pitcher age 36 or older had a WAR of at least 7.4. Now let’s move the calendar forward. Just 14 times has a pitcher age 37 or older put up a WAR of at least 7.4. Of those 14 seasons, four came in the Deadball Era, and another two came before World War II. The eight remaining seasons belong to just four different pitchers — Randy Johnson (3), Phil Niekro (3), Roger Clemens, and Curt Schilling. In other words, it’s rare to do what Verlander did last year, but it’s significantly rarer to do what he’s trying to do in 2020 — i.e., be as good as he was last season at age 37. (Never mind that the abbreviated length of the 2020 season, should it come to pass, will make it all but impossible for a pitcher to have such a WAR — the point stands on a rate basis.) 
So we’ve got some peripherals that suggest that Verlander wasn’t quite as good as his 2019 ERA would lead you to believe, and we’ve got signs of decline in velocity, spin rate and his ability to locate. On top of all that, Verlander is, to repeat, 37 years of age. It’s rare to even have a major-league career at that age, let alone thrive. 
95.6 mph
Then there’s the matter of command. Over at Baseball Prospectus, they’ve developed the “called strikes above average” (CSAA) metric, which is a good statistical proxy for what we mean we talk about a pitcher’s command. Note this mini-trend:
2018