The Mariners did not emerge from the Winter Meetings as one of the big movers and shakers, but they did address their move obvious need. They entered the offseason lacking rotation depth, and in trading Taijuan Walker to the Diamondbacks in last month’s Jean Segura deal, they left themselves even more strapped for starting pitching. By acquiring Chris Heston from the Giants for a player to be named later on Wednesday, they added an experienced starter whom they could plug right into their rotation.
While the Mariners needed to add depth, it’s not as if they replaced Walker. Any of the top three candidates for the final two spots in the rotation — Heston, Nate Karns and Ariel Miranda — could top Walker’s 4.22 ERA from 2016, but none can match his pedigree. Baseball America ranked Walker among their top-20 prospects three years running, and at times, it looked as if he was on the verge of living up to that potential.
In his first five starts of 2016, Walker compiled a 1.80 ERA with 29 strikeouts and three walks allowed in 30 innings. He had a four-game stretch with similar ratios in June, and a seven-game run in 2015 that produced a 1.68 ERA and a 51-to-3 strikeout-to-walk ratio.
Had Walker remained with the Mariners, he might have developed the sort of consistency that would have made him one of the team’s top three starters. If Heston, Karns or Miranda pull off that feat, it would probably be because Felix Hernandez or Hisashi Iwakuma failed to rebound from disappointing seasons, and not because they had a sudden spike in performance.
Nonetheless, Heston can make an important contribution by providing higher-quality innings at the back of the rotation than Wade Miley or Karns did last season. Even so, unless Hernandez and Iwakuma rebound and James Paxton builds on his 2016 breakout, the Mariners’ rotation may be no better than a middle-of-the-pack unit. This past season, their collective 4.25 ERA was just 12 points below the major league median for rotations.
The Mariners may lack the front-of-the-rotation firepower possessed by the Indians and Red Sox, but now they are at least better positioned to compete within their own division. Though they don’t have a 1-2 combination like Yu Darvish and Cole Hamels, the Mariners’ rotation compares favorably with the Rangers’ once you get beyond the top two. Also, Seattle’s rotation bears some similarities to Houston’s. Both groups are led by former Cy Young award winners — Hernandez and Dallas Keuchel — coming off a down season despite being in their peak years. Lance McCullers, like Paxton, had some promising peripherals that had to be weighed against health issues and a lofty BABIP rate. And both teams have the option to fill out the remainder of their rotations with veterans who have had past success but modest upside.
To assert that Iwakuma, Heston, Karns and Miranda lack upside isn’t to say that they can’t be part of a competitive rotation. Heston, in particular, has shown that he can be a reliable No. 3 or 4 starter. He was an unexpected addition to the Giants’ rotation during the first week of the 2015 season, but he pitched well enough to stick around and make 31 starts. Through the first 20 of those, Heston registered a 3.14 ERA and allowed only six home runs over 126 innings. Though Heston had the advantage of playing home games in pitcher-friendly AT&T Park, he didn’t need it, as he allowed ground balls at a 56.5 percent rate over those first four months, according to FanGraphs. He relied heavily on a sinker that yielded an .066 Isolated Power over that stretch (per Brooks Baseball).
Since then, it’s been a downward spiral for Heston. He lost velocity and control over the latter third of the 2015 season, and his velocity dipped further still in early 2016. He started the year in the Giants’ bullpen, but was soon demoted to Triple-A Sacramento. Just as soon as he started to get into a midseason groove, Heston landed on the disabled list with a strained oblique.
So while Heston is merely average as a strikeout and control pitcher, at his best, he can be well above-average as a run-preventer. Whether or not he will arrive at spring training with better health and greater velocity remains to be seen.
Iwakuma may no longer be a good bet to get his ERA back down into the low-to-mid 3.00s, but he can certainly be better than he was in 2016. In fact, for the latter half of the season, he wasn’t much worse than he had been in the previous two seasons. In slowing down the barrage of home runs that hurt him over the first three months, Iwakuma compiled a 3.74 ERA over his final 16 starts.
As for Karns and Miranda, each has a strength that could play well in the American League West. Karns has pitched with reverse splits over the course of his career, and that should serve him well against the Astros, who added three lefty bats and switch-hitting Carlos Beltran this offseason, and the Rangers, who have several key lefties in their lineup. Miranda is a fly ball pitcher who proved to be effective at getting outs on balls in play, particularly in the form of popups. The Angels, Athletics and Rangers are all teams who put the ball in play. That hasn’t been the case for the Astros in recent years, but with the additions of Beltran, Josh Reddick and Nori Aoki, that should change.
Because he is a year removed from a successful season that included a no-hitter, Heston got more notice than the pitchers the Mariners acquired in the recent deal that sent Alex Jackson to the Braves, but they could also play an important role in 2017. Rob Whalen did not have an auspicious major league debut last summer, but like Heston, he was able to use his sinker to induce grounders. Max Povse is a strike-throwing 23-year-old who could be ready for his debut later in the season. Add in fellow righty prospect Andrew Moore, and suddenly, the Mariners could have a surplus of major-league ready starters by midseason.
While the Mariners no longer lack for quantity in their starting pitching corps, they still do not have the quality to match up with the top teams in the American League. As the injury-plagued Indians showed during their postseason run, that doesn’t necessarily preclude the Mariners from making a legitimate run at the World Series. With the addition of Jean Segura and a full season of Mike Zunino, they could upgrade an offense that finished sixth in runs scored in 2016. If Steve Cishek has a successful recovery form hip surgery and Evan Scribner can stay healthy, they could help Edwin Diaz to shorten games and take some of the load off the rotation.
Of course, that represents the best-case scenario. If Walker reaches his potential, it’s hard to say that the Mariners would have a better rotation without him. In his absence, though, the organization has done an admirable job of improving the back end without compromising their short- or long-term chances of competing.