Will James Paxton Emerge as the Mariners' Ace in 2017?

There hasn't been any question over the years as to who the ace of the Seattle Mariners pitching staff has been. James Paxton will try to grab that title this season, though.

Since bursting onto the scene in 2005, Felix Hernandez has been the unquestioned ace of the Seattle Mariners. Although he could be due for a bounce-back season, he's entering his age-31 campaign and it might be time for someone else to take on the role as staff ace.

Who has the ability of doing just so in 2017? That'd be southpaw James Paxton.

One-Year Wonder?

Paxton turned a lot of heads last year, which was by far his best single-season performance since debuting in 2013. It's not as if we really couldn't see this coming, though.

The below table looks at his performance in the two years leading up to this breakout of sorts, and he had some nice underlying numbers despite a disappointing 2015 before putting it all together in 2016.

His strikeout rate (K%) increased, his walk rate (BB%) was basically cut in half, and his ERA+ hung right around league average (which is 100). However, his ERA+ being that high was more due to things out of his control (like team defense), which is evidenced by his very low xFIP- (average is also 100).

2014 19.50% 9.60% 120 93 3.54
2015 18.90% 9.80% 98 108 4.35
2016 22.90% 4.70% 107 79 3.35

For some reference, that xFIP- of 79 would've ranked fourth-best last season among qualified pitchers, trailing only Jose Fernandez, Noah Syndergaard and Michael Pineda. So, how did the left-hander go from being a good pitcher to performing like a top-tier hurler (albeit in fewer innings) in 2016?

One Big Difference

A change in Paxton's pitching motion was the biggest difference between his performance between 2014 and 2015 compared to last year. With this new motion came a better cutter, which is illustrated below, courtesy of Innings Pitched.

According to PITCHf/x, Paxton threw his cutter at an average velocity of 89.9 miles per hour, which is around what's it's been throughout his young career. The difference was his usage -- he threw it a career-high 15.7% of the time last year -- and the actual results.

Over the past three years, the value of this pitch went from -1.1 to -0.2 to +8.1. Paxton's cutter has also evolved into his best overall pitch.

Year K% BB% wRC+ against Cutters
2014 10.00% 10.00% 205 34
2015 0.00% 33.30% 148 29
2016 34.80% 1.10% 29 325

The new motion did not just give him an elite cutter, though. It gave him the ability to throw 99 mph on the black.

Another product of his new motion was an increase in average fastball velocity. He averaged 94.2 mph during the 2015 season, but that number jumped to 96.7 mph last year, which can go a long way in keeping opposing hitters off balance.

The Big Red Flag

This all makes it sound as if he's set up to lead the staff at Safeco Field and compete for the AL Cy Young award. That could very well be in his immediate future based on talent and recent performance, but the southpaw has to stay on the field to make it possible.

The only time he's accumulated more than 13 starts in a year came in 2016, when he started 20 games, which also included a career-high 121 big-league innings. So, it seems as if the only thing keeping him from having a true breakout campaign is his health.

But if he's able to combine his new motion and impressive production while staying healthy for at least 170 or 180 innings, he could be one of baseball's toughest pitchers to hit this season.