At the outset of the season, the lines were clearly drawn with regard to the Yankees' rotation. Masahiro Tanaka was the ace. CC Sabathia, after bouncing back with a strong 2016 season, was the wily, dependable veteran. Michael Pineda was the undependable veteran, whose mix of brilliance and frustration would inevitably leave him around average. At the back of the rotation were a couple of youngsters, Jordan Montgomery and Luis Severino, that were difficult to peg.
Baseball, of course, turned everything upside-down. By midseason, Pineda was out with Tommy John surgery. Tanaka's ERA was closer to nine than it was to three. Montgomery had emerged as one of the Yankees' steadiest hands. Most surprisingly of all, though, was Severino's development into one of the game's best pitchers.
It's not an exaggeration to say that Severino wasn't just the Yankees' Cy Young for the year, but one of the top pitchers in all of baseball. He came out of the gates throwing far better than anyone expected, and kept up his shocking pace all season. In a league that didn't include peak versions of Corey Kluber and Chris Sale, Severino would've been a genuine contender for the AL Cy Young award.
Severino won't win the actual Cy Young this year, but after a 2017 season that saw him break out, there's no question he will be a popular pick to procure such an honor in coming years. He was, by distance, the Yankees' best pitcher in 2017. He logged 193.1 innings over 31 starts. His sparkling 2.98 ERA equated to a 152 ERA+, third-best among AL starters. He struck out 230 batters, and walked just 51.
Total value metrics naturally held Severino in high regard. His 5.7 fWAR was fourth in baseball and third in the AL. His 5.4 WARP was third in the AL, and his 5.3 rWAR was sixth in the AL. No matter how you slice it, Severino was an ace.
There's plenty about Severino's season that was remarkable, but what may be most notable is how surprising it really was. Hopes were still high for Severino entering the year based on his precocious talent, but after a terrible 2016 in which he performed better as a reliever than as a starter, it wasn't clear where Severino's future role was. 2016 saw Severino record a 5.83 ERA with mediocre strikeout and walk totals. That Severino was bouncing back from such a poor year made his 2017 season all the more shocking.
There's no one smoking gun that reveals why Severino was able to improve so dramatically. Rather, it was more likely an amalgamation of things, a number of improvements Severino made that led to a great year. That said, Severino has pointed to offseason work he did with Pedro Martinez to slow himself down and better simplify and repeat his mechanics.
It's impossible to tie down all of Severino's success to some winter work with a pitching legend, but it does seem like a focus on cleaner mechanics helped Severino. On the surface, his control improved. His walk rate fell, and his strikeouts rose.
Moreover, his location just seemed better. From Baseball Savant, take a look at where Severino located his fastballs, first in 2016, and then in 2017:
Here's the location of his sliders in 2016 and 2017:
You'll notice the shift towards the bottom of the zone with his slider, and towards the top of the zone with his fastball. This makes sense; pitchers generally want hitters chasing down at their breaking pitches and swinging up at their fastballs. To wit, Severino's whiff rate on both his fastball and slider rose this year, per Brooks Baseball.
Smoother mechanics may have also helped Severino fully unlock his hard-throwing potential, as Severino came in with higher velocity and sustained it all year. According to Brooks Baseball, Severino was actually throwing harder in September and October (at 98.1 mph on average) than he had all year.
We haven't even mentioned Severino's changeup, which he increased in usage from 8% to 13%, giving hitters another weapon to worry about. Again, it doesn't seem like there was one thing that led to Severino's improvement. He really just seems to have gotten better in various ways, all helping him to succeed like never before.
In short, Severino became the hardest-throwing starter in the game, used his changeup more, and started locating his pitches better to avoid home runs and walks and generate more whiffs. He was simply a more complete pitcher. He had more weapons to turn lineups over multiple times, better control to limit mistakes, and more firepower that held him deep into games.
Severino is the clear choice for the Yankees’ Cy Young for 2017. Barring some starry free agent signings like Shohei Otani or Yu Darvish, Severino will probably be the favorite to be New York’s best pitcher in 2018 and beyond as well. At just 23 years old, Severino has already turned into a great pitcher. If he can keep this up, the Yankees will truly have something special on their hands.