Last season, optimism abounded with the Mariners' rotation. The acquisition of J.A. Happ, combined with the presumed ascendance of Taijuan Walker and James Paxton, seemed to point to a solid top-to-bottom group that could compete to be the best in the American League.
Then reality struck. Injuries wiped out much of Iwakuma and Paxton's campaigns, and Walker struggled after a solid spring. King Felix posted his lowest fWAR since his rookie year, and Happ was simply a fine back-end starter until he was traded to Pittsburgh in July (at which point, in typical Mariners fashion, he rebounded to post a 1.85 ERA with the Bucs). The Mariners finished 17th in the majors in FIP at 4.18 en route to a disappointing 76-86 mark.
But 2016 brings renewed optimism. There are signs for positive regression, as the M's rotation had the 4th-highest HR/FB rate in the league last season at 13.6%, which contributed to the single largest difference between a team's rotational FIP- (106) and xFIP- (96) in 2015. After injuries tanked much of last season's hope, new general manager Jerry Dipoto has combined his own moves with trades made by his predecessor, and the result is depth that figures to keep the Mariners afloat even in the stormiest of seas.
When discussing the M's pitching staff, tradition dictates that you must start with the King. Felix Hernandez turns 30 in just a few weeks, but the Venezuelan ace remains dominant. It's only fair to note that his HR rate did increase last season to the highest it has been since his sophomore campaign (1.03 HR/9, compared to a 0.73 HR/9 career rate), and his arm has been used early and often, topping 200 innings for the eighth straight season last year. But projections have him as between a 4.5-5 WAR player, and there's no reason to expect him to collapse. Felix is as special a pitcher as there is, and we're lucky to be able to watch him every fifth day. Do be aware of the hideous blond hair/beard combo, however. It's not a good look, FiFi.
Hisashi Iwakuma delivered one of the best Mariners moments in recent memory last year with his dazzling no-hitter against the Baltimore Orioles. Perhaps his second-best moment for Mariners fans was when it was announced (at the Mariners' holiday party, no less) that he was returning to Seattle following a failed physical that nullified a multi-year pact with the Dodgers. His contract, a one-year deal with vesting options for 2017 and 2018 depending on innings pitched, is very low risk for the Mariners, but he's never been close to the workhorse that Felix is (though, then again, who is?). If Kuma can make 30 starts this year, he'll be roughly a three-win player and will make Mariners fans very, very happy.
Taijuan Walker's 2014 season and his spring training a year ago gave fans every reason to dream, and his top-prospect pedigree seemed to indicate a breakout campaign. Viewed in that light, Walker's 2015 was surely disappointing; however, given that last season was his age-22 season and he was somewhat unlucky, with a 67.8% strand rate, it's more accurate to view it as a stepping-stone year.
His powerful fastball will always translate, and if he can keep his homer rate down, he could easily make the leap that so many expect of him. Colin O'Keefe wrote about Walker's increased curveball usage last year, and if Walker can continue to combine that with his mid-90s heater and changeup, that leap could be exactly what fans have been waiting for.
Wade Miley figures to hold down the fourth spot in the rotation. Acquired from Boston in a trade for Carson Smith and Roenis Elias, Miley is an innings-eater, with at least 29 starts in each of his last four seasons. The lefty should benefit from a move to Safeco after spending 2015 in hitter-friendly Fenway and provides a solid, albeit unspectacular, option at the bottom of the rotation. He's under team control through 2018, so expect to see him and his deep five-pitch repertoire in a Mariners uni for years to come. His fastball hovers between 91-92, and he mixes in a lot of sinkers and changeups. Jake wrote a great article in December discussing more of Miley's pitch usage in depth.
The fifth spot in the rotation is up for grabs, with two main pitchers - James Paxton and Nate Karns - competing for the role as we speak. Paxton has shown promise but has largely underwhelmed at the major-league level, fighting through a string of unrelated, unrelenting injuries. Karns was added in a deal with Tampa Bay in the offseason coming off his first full season in the bigs at age 27. The former Ray has certainly out-performed Paxton this spring, but there is no word yet who will win the battle (though my money is on Karns).
Though Karns is a righty and Paxton a southpaw, the two have similar builds; Karns is 6'3", 225 lbs and Paxton weighs in at 6'4", 235 lbs. Both have fastballs that hit right around 94 miles per hour, but the difference between the two lies in their usage. Karns throws his fastball between 40-45 percent of the time, mixing in curves, changeups, and sinkers. Paxton, however, throws his heater a whopping 65-75% of the time! Developing offspeed pitches will be crucial to his development.
Those six players will cover the five rotation spots, but last year certainly proved that depth is also essential, and Mike Montgomery and Vidal Nuno are great players to have in that capacity. Both are likely to start the season on the big-league roster in the bullpen. Montgomery shocked basically everyone when he threw back-to-back shutouts last season, and if he can find that form that escaped him as the season went on - perhaps because his fastball usage went from 27% in June to 45% in August - he's certainly a valuable piece.
Nuno, on the other hand, lacks the former top-prospect sheen of Montgomery, and it's not hard to figure out why, since his fastball hovers just around 90. But if he can effectively use his slider, changeup, and curveball to complement his fastball, he can make spot starts from time to time.
Fangraphs projects the Mariners' rotation as the #13 group in the bigs and the sixth-best rotation in the AL. It's a reasonable projection, to be sure, but I see a lot of upside here as well given the youth of pitchers like Walker, Karns, and Paxton. If the squad finds itself playing in October this season, the rotation will be a big part of the reason why.