Clayton Kershaw was baseball's best pitcher in 2015

Yesterday, we kicked off the SB Nation MLB awards with my vote for Bryce Harper for baseball's hitter of the year. Today, we'll cover pitcher of the year. I'm still taking nominations for the next three categories:

Wednesday: Pirates' best defensive play of the year
Thursday: Pirates' best celebration of the year
Friday: Best breakage of the unwritten rules (in all of MLB)

My vote for pitcher of the year is Clayton Kershaw.

My first thought was to pick Jake Arrieta, on the grounds that his brilliant end-of-season run should give him the tiebreaker if his overall performance was similar to Kershaw's -- the award is for the entire year, but if I could find a compelling reason to reward Arrieta for basically being unhittable for an entire half of a season, I was going to take it. And, of course, Arrieta did finish almost two-fifths of a run better than Kershaw in ERA (although he was behind Zack Greinke in that category).

The thing is, though, as great as Arrieta was, I'm not sure his performance really was all that close to Kershaw's. Arrieta was, in addition to all his other obvious virtues, a ground-ball machine this season. The contact he induced was also a bit softer than Kershaw's.

But most of the two pitchers' other underlying numbers point decisively in Kershaw's favor. Kershaw struck out well over two batters more per nine innings than Arrieta did, which is a massive difference -- the gap between Kershaw's 11.64 K/9 and Arrieta's 9.28 is almost as big as the gap between Arrieta's and Jeff Locke's (although, of course, as we discussed in the comments, some of Arrieta's relatively low K/9 is that he got through innings so efficiently and faced so few batters). Kershaw walked batters at a lower rate than Arrieta did, as well. It's no surprise, then, that FIP, xFIP and SIERA all favor Kershaw, and by a large margin.

From the perspective of stuff, too, Kershaw's candidacy is tough to dispute. He isn't exactly known as a fastball pitcher, but via Pitch Type Linear Weights, his fastball was the most valuable pitch in baseball last year. (Gerrit Cole ranked second, with Arrieta third.) It would be one thing if Kershaw combined that fastball with only one terrific breaking ball, but he has two. His famous curveball rated as the third-best in baseball last year, behind only Felix Hernandez and Corey Kluber. His slider, meanwhile, was the seventh-best in the game. (Francisco Liriano's was the best.) Just try hitting this thing.

In other words, Arrieta was ridiculous. But Kershaw was even more ridiculous. And the main reasons that wasn't obvious was that Kershaw's batting average on balls in play was higher, and that Arrieta got more wins.

Cole, by the way, had a brilliant season of his own, and it's a shame that Kershaw, Arrieta, Greinke and others pitched so well that he isn't even really in the conversation. Fortunately, he recently turned 25, and he could have plenty more elite seasons ahead of him. There aren't many pitchers whose upside is seasons like the ones Kershaw and Arrieta just had. Cole is one of the few.

Honorable mentions: Arrieta, Greinke, Max Scherzer, Dallas Keuchel, David Price