Should you believe in James Paxton?

A look at the Fangraphs pitching leaderboard for the second half of 2016 reads — for the most part -- like a who’s who of dominant starters. At the top are the respective Cy Young Award winners in each league: Rick Porcello and Max Scherzer. Further down the list you’ll find oft-discussed breakout candidates like Ivan Nova.

But right there, just ahead of superstars Yu Darvish and the late, great Jose Fernandez, is Mariners left-hander James Paxton.

It’s certainly surprising to see Paxton up there in ace territory, even if we’re just looking at one three-and-a-half month stretch. He’s been good at times in his career. Yet, your instinct is probably to say that this was more fluke than anything.

Well, I am here to change your mind. To an extent, at least. I don’t think he’ll be one of the ten best pitchers in baseball, as he arguably was after the All-Star break. But there is a case to be made that the effectiveness Paxton has shown in short glimpses is sustainable over a full season.

So let’s start with what worked in 2016. The most encouraging sign from Paxton’s season was his improved command.

League-wide, starting pitchers allowed 2.96 walks per nine innings in 2016. In neither 2014 (3.53) nor 2015 (3.90) had Paxton come all that close to approaching league average walk limitation. But this year something apparently clicked, and his walk rate dropped to a minuscule 1.79 batters per nine. That put him ahead of noted control artists like Kyle Hendricks and Phil Hughes.

His general approach didn’t change all that much. The goal was still to pitch down-and-in to righties and low-and-away to lefties. Here’s his 2016 zone profile, per Brooks Baseball:

BrooksBaseball.net

Now compare that to his career zone profile (2013-15) coming into the season:

BrooksBaseball.net

Paxton did a much better job of keeping those pitches in the lower left portion of the chart, but also of staying within the strike zone. He elevated the ball enough to force batters to swing at it, but not so much that he left himself open to further damage near the heart of the plate.

This started early in an at-bat, as Paxton -- for the first time -- posted an above-average first pitch strike percentage. Before 2016, there was a slightly better than 50-50 chance that Paxton’s first pitch would be in the zone. This year, he started batters off with a strike 62.6% of the time, above the league average of 60.3%. That makes a real difference, especially when you have the type of stuff Paxton has (which we’ll get to).

And when he did go out of the zone? Paxton set a career high in both O-Swing% (the percentage of pitches outside the strike zone a batter swings at) at 32.0%, way up from 2015’s 21.3%. Because Paxton’s opponents had to respect his newfound command, they were much more willing to chase for fear of getting (further) behind.

You would certainly like to see Paxton do it again before you go all in, but that’s the kind of thing improved command can do for a pitcher. By throwing regular strikes -- particularly quality strikes -- Paxton forced hitters to adjust to him, rather than the other way around.

If it were just command that led to Paxton’s 2016 improvement, that would be encouraging in and of itself. But here’s another reason to get excited about him in 2017: his stuff was better than ever.

BrooksBaseball.net

That’s a chart of Paxton’s year-by-year velocity, again from Brooks Baseball. As you can see, he threw harder in 2016 -- at age 28 -- than he ever had at any point as a major leaguer.

Paxton’s fastball was the third-hardest among starters with at least 50 innings pitched in 2016, trailing only Noah Syndergaard and Nathan Eovaldi. But interestingly enough, despite throwing the ball harder than ever before, Paxton used his secondary pitches more than any other point in his career:

BrooksBaseball.net

A mostly new addition was a 90 MPH cutter, something Paxton had toyed with in previous years but didn’t fully commit to until this season. And that commitment was with good reason, as batters hit .189 against the pitch, while whiffing about a fifth of the time, per Baseball Savant.

That cutter, along with a slightly less effective curveball and the aforementioned fastball, give Paxton three above-average pitches he can rely on. It also allows Paxton to continue to fade out an ineffective changeup.

Having three reliable pitches is generally the difference between starting and being punted to the bullpen. You can get away with just two coming out of the bullpen, but going through a batting order multiple times becomes more difficult when you can’t rely on an effective third pitch. For now, it appears that Paxton has found one.

If you’re looking to be optimistic about Paxton in the future, you will also want to analyze his fielding-independent numbers. It turns out, for all of his improvements in terms of stuff and command, Paxton may have actually gotten a bit unlucky last season.

Paxton’s ERA (3.79) was nearly a full run higher than his FIP (2.80) in 2016, primarily because of a .347 BABIP that was well above the league average of .298. Some of that can probably be explained by the Mariners poor defense -- 22nd in the league, according to Fangraphs metrics -- but a large portion was probably simple bad luck.

The question hanging over all of this is: can Paxton do it again, and over a full season? While 2016 was his longest stretch of sustained effectiveness, he’s shown flashes before only do disappoint and start the cycle anew.

He didn’t make his 2016 debut with Seattle until June of this year because he was such a train wreck in spring training the Mariners felt compelled to Triple-A. Does he lose velocity over the course of the offseason? How about command? Can he continue to maintain his reverse platoon splits?

Those are all questions we won’t have answers to for a while. In the meantime, Paxton will remain a bit of an enigma. Doubting him is fair -- he still hasn’t shown us that much. But if you want to finally go all in? Well, 2016 was a pretty good start.