In 2015, Sonny Gray was the A's lone shining light. After a rookie season in which Gray's electric stuff lit up the playoffs and a second season in which he took another step forward, Gray seemed to solidify himself as an ace in 2015, finishing third in Cy Young voting. There were some questions regarding Gray's ability to miss bats and his stamina as he faded down the stretch, but there was never a doubt that he was an asset.
Then, 2016 happened. Gray was downright bad and a guy who was once the cornerstone of a young rotation was the leading cause of disappointment for a team that couldn't do anything right.
One of the first questions you have to ask when thinking about the viability of a 2017 playoff run is which Gray will we get. The difference between Gray's 2015 and 2016 is the difference between an ace and a fringe major leaguer, and could easily be the difference between 82 wins and a playoff berth. What does history have to say?
The power of the Play Index
If you're a fan of baseball history or of throwing hours of your life down an internet rabbit-hole, the Play Index from Baseball Reference is for you. With the power of said tool, we can look at all the players similar to Sonny Gray. I defined that as players who put up between 5-8 bWAR in a single season before their age 27 season and followed said season with a season worth 1.0 bWAR or less, since the DH era began in 1973. It's a bit arbitrary, but it should give us a nice idea of how common or rare this is while also not taking hours on end for me, which I know is most important for you. Basically, we're looking to see how often young pitchers fall off a cliff, and how they respond in the season following.
How often has a pitcher pulled a Sonny Gray?
I've defined pulling a Sonny Gray as a starting pitcher who put up 5 or more bWAR but less than 8 bWAR in a single season before the age of 27, then following it up with a season of 1 or fewer bWAR. That's to make sure the pitcher is nearly elite and young, and should signify that the dropoff isn't the result of a pitcher being past his physical prime.
With that loose definition of "pulling a Sonny Gray" in mind, there have been 19 instances of pitchers doing so since the DH was implemented in 1973. Of those 19, ten never recovered, six turned into serviceable, albeit lesser pitchers, and three returned to their former glory.
As a reminder, this is how Sonny Gray's past two seasons have gone.
2015: 5.8 bWAR, 31 GS, 208 IP, 2.73 ERA, 7.3 K/9, 2.6 BB/9
2016: -0.5 bWAR, 22 GS, 117 IP, 5.69 ERA, 7.2 K/9, 3.2 BB/9
The tragic cases
I've read enough Harry Potter to know you always end on a positive note, so let's start out with some of the sad, cautionary tales. Of the 19 players fitting the criteria, 10 didn't return to any level of success. They are Roberto Hernandez, Ricky Romero, Matt Harrison, Steve Busby, Craig McMurty, Matt Young, Mike Norris, Jhoulys Chacin, Oliver Perez, and Joe Kennedy (Rest in Peace).
Season 1: 6.3 bWAR, 32 GS, 225 IP, 2.92 ERA, 7.1 K/9, 3.2 BB/9
Season 2: -1.4 bWAR, 32 GS, 181 IP, 5.77 ERA, 6.2 K/9, 5.2 BB/9
A common theme among players on this list is a lack of control. That makes sense, as to attain a 5 bWAR season, you have to have great stuff and to attain a season with less than 1 bWAR with that kind of stuff, you have to have a major problem. That problem has often been an inability to locate, and Ricky Romero went from electric starter to guy who couldn't hit the broad side of an Angel Hernandez strike zone.
Like Gray, Romero was known for his electric stuff and most believe there was never a physical ailment that caused his demise. While Gray did see an increase in walks, his demise wasn't entirely control based: he still threw strikes, by and large.
The return to serviceable
Of the 19 pitchers to pull a Gray, 6 of them returned to being serviceable. This again is a bit arbitrary, but all of these guys were fixtures in starting rotations, putting up average numbers and overall being assets but not stars. They include: Bob Knepper, Jim Clancy, Bob Forsch, Ervin Santana, Melido Perez, and Jair Jurrjens.
Season 1: 5.0 bWAR, 32 GS, 219 IP, 3.49 ERA, 8.8 K/9, 1.9 BB/9
Season 2: -0.2 bWAR, 23 GS, 181 IP, 5.03 ERA, 6.9 K/9, 3.0 BB/9
As an A's fan, you might be surprised to see just how unremarkable Ervin Santana's career is in spite of his routine domination of the green and gold. Santana has lasted as a mid rotation guy after showing flashes of brilliance early in his career, and he's absolutely an asset to his team. He's just not a star.
The return to glory
Sadly, there are only three cases of pitchers returning totally to their top form in our sample. Those players are Jerry Reuss (5.4 bWAR followed by 0.6 bWAR), John Denny (5.2 bWAR followed by 0 bWAR), Charles Nagy (6.1 bWAR followed by -0.4 bWAR).
Season 1: 5.4 bWAR, 32 GS, 2.54 ERA, 5.0 K/9
Season 2: 0.6 bWAR, 29 GS, 3.53 ERA, 4.6 K/9
Career following: 14 years, 19.9 bWAR
True to the era, Reuss was an absolute workhorse. pitching in 22 total season at the big league level. It would take a few years for Reuss to re-find his form, but once he did, he was a front of the rotation type guy, finishing his career with 220 total wins. Yes, I just cited wins.
As for the other two, their bad seasons both came as the result of injury: for Nagy a torn labrum, and for Denny a torn hamstring. Nagy returned to make a couple All-Star teams, and Denny won a Cy Young.
All baseball players are unique flowers
So, the track record for having a year like Sonny's 2016 and returning to ace form isn't great. But all baseball players are unique, and each of these hurlers took his own individual path that will differ from whatever Sonny's ends up looking like. History is a guide, not a guarantee, and Sonny's chances should be judged on things like whether you think he'll stop hanging pitches up for dingers and keep himself off the DL.
But maybe keep your expectations tempered, just in case.