Life is full of mysteries, and so is baseball. This week, as part of The Ringer’s 2017 MLB Preview, we’ll be taking a closer look at some of the most intriguing people and teams entering the season. Some excite us, some confound us, but they all leave us asking the same question: What’s Your Plan?

Since Jerry Dipoto took over as Mariners general manager in September 2015, he’s presided over the departure of all but nine members of the 40-man roster he inherited. His trade activity has dwarfed any other executive’s to such an extent that my podcast cohost wrote a musical ballad about it. Seattle’s projected depth chart reveals that since last season alone, Dipoto has dipped into the trade market for new first, second, and sixth hitters, a fourth and fifth starter, and other assorted spare parts.

Yet after all the turnover, the Mariners’ latest attempt to end their playoff appearance drought — now at 15 years, the most prolonged in the majors — depends as much as anyone on the team’s longest-tenured player, Félix Hernández. It would be too simplistic to say that Hernández’s season will determine the Mariners’ fate, because baseball doesn’t work that way. Félix could be bad and the Mariners might win anyway; Félix could be the best pitcher in baseball and the Mariners still might miss the playoffs. (It’s happened a time or two before.) But the return of the King — which Félix’s trainer has turned into a hashtag — would probably benefit the Mariners as much as or more than any addition Dipoto made this winter.

To recap: Hernández is coming off what was by most measures the worst of his 12 major league seasons. An uncharacteristically low BABIP helped hide his declines across several categories, including a career-high walk rate and a career-low strikeout rate — the latter of which was especially notable for a pitcher whose big league career has spanned a period during which the average qualified starter’s strikeout rate has risen by 23 percent. Hernández allowed runs at a rate slightly below the league average, but among the 84 pitchers who totaled at least 150 innings, his ballpark-adjusted fielding independent pitching tied for 16th worst.

Hernández, who hasn’t yet turned 31, is nearing 3,000 innings pitched as a professional. Barring any serious injuries, which he’s largely avoided thus far — last season’s calf strain, which forced him to wear a walking boot, led to the longest absence of his career — he’ll hit that mark in 2018. Although the M’s were always conscious of protecting his arm, fully letting him loose only after he exited the so-called injury nexus, it’s tempting to conclude that Hernández’s past workload has handicapped his future. All else being equal, though, pitchers who’ve piled up innings and pitches are as likely to keep doing so as anyone else.

The most obvious culprit behind the King’s decline is his transition from flamethrower to soft-tosser.

In 2007, the first year for which we have any PITCHf/x data, Félix threw harder than any other starter, besting the next-fastest pitcher with at least 100 four-seamers tracked (Ubaldo Jiménez) by more than a mile per hour. (Noah Syndergaard last year is the only pitcher to top Félix’s 2007 fastball speed in the nine seasons since.) Last season, throwing almost 7.5 mph slower, Félix tied for 179th out of 228. His fastball speed doesn’t look like it once did, so it makes sense that his stats don’t look like they once did, either.

Given the magnitude of that drop, it’s impressive that Félix is still pitching at all. In the PITCHf/x era, no other starter with at least 100 pitches thrown has had two seasons separated by such a wide margin in average fastball velocity. The guys with the next-greatest gaps all are, or were, on their way out in the lower-velocity season: Jered Weaver, Chris Young, Tim Lincecum, Ubaldo, Jake Peavy, Dan Haren, Justin Masterson. Most pitchers couldn’t lose 7.5 mph and still be in the big leagues because they don’t have that far to fall. That Félix could is a testament to how hard he once threw, and how good he once was.

Still, this seems like a crossroads for the King. If his stuff keeps slipping and last year’s luck doesn’t hold, he could be headed for a Lincecum-like early exit from the sport. But if his fastball rebounds or he finds some way to succeed at reduced speed, he could still have a productive back end of his Hall of Fame–worthy career, even if another Cy Young–caliber season remains a stretch.

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Let’s examine each of those possible paths to salvation. The first is simple: Félix finds his fastball. Hernández was elite as recently as 2014, when his four-seamer and sinker averaged 93.6 and 93.0 mph, respectively, a little more than two miles per hour faster than they flew last season. Félix’s command and mechanics have also eroded since then, but M’s fans can at least dream about what he could do with two ticks restored to his speed.

Demographically speaking, Félix seems like a bad bet to get his heater back. As a group, pitchers tend to start losing speed almost from the moment they make the majors, and Félix has reached the region of the aging curve where the decline often comes quickest. Once a pitcher loses significant speed, it rarely returns: FanGraphs writer Bill Petti found that only 7 percent of pitchers who lose one mile per hour or more from one season to the next regain any velocity in the following year. The odds get even longer for older pitchers, and it can’t help Hernández’s chances that he’s suffered such dips in multiple years. Even worse, he’s also reached the age at which that decline often becomes particularly costly: The Hardball Times’ Mike Fast found that pitchers in their early 30s tend to be more sensitive to changes in fastball speed than pitchers in their late 20s, possibly because they’ve run out of alternative tactics to compensate for eroding velocity. History says Félix is screwed.

But there is one reason to think that looking at the whole population of pitchers might underrate Félix’s chances of a temporary reversal — a wrinkle in the trend line between his heyday and the far-off future when he’ll accept nostalgic standing ovations and bounce ceremonial first pitches from a spot in front of the mound. Félix, this winter, worked hard.

Because Félix was so skilled from the start, he has never been known for preparation. He didn’t have to memorize scouting reports or adhere to a rigorous workout plan, because his natural ability made him better than the pitchers who did. It’s not as if he never exercised — over the 2006–07 offseason, he dropped 30 pounds, and as recently as two years ago he talked about entering spring trimmer than he’d been the year before. But unlike most of his peers — the pitchers who make up the aging curve that Félix will try to defy — he hadn’t devoted himself to a strength-building program. That means that Félix has something most veterans with his workload and diminished stuff don’t: upside.

Last year, the Mariners openly criticized Félix’s 2016 season, listing the ways in which he had to improve his approach and physique. In response, the pitcher picked up the gauntlet, vowing, “I’m going to show everybody that doesn’t believe in me that I’m still Félix.”

This spring, he showed up with more muscle, an accelerated throwing program, and encouraging quotes from his trainer about the flaws he fixed in the kinetic chain. It all sounded consistent with a return to form, but we never know how much to make of the annual outpouring of weights and words that follows the first flickers of baseball. It’s easier to exaggerate the benefits of fitness plans than it is to distort TrackMan readings, which is why the most positive sign so far has come not from Félix’s mass, but his miles per hour.

Last March, Félix’s four-seamer sat at 91.1 mph, and his sinker was clocked at 90.8. In his first recorded outing of this spring, his speeds were up to 91.5 and 92.2, respectively. Both numbers are higher than his full-season figures from last year, which is especially impressive because Félix, like most pitchers, tends to pitch with higher velocity as the weather warms up.

That’s just one short outing and one measurement system; we should get more data from Félix’s work in the WBC. But if he’s already ahead of where he finished last year, the dream of a faster Félix isn’t dead.

Even if that apparent fastball bump doesn’t survive into the season, there’s the hope that Félix could tinker until he finds a strategy better suited to his 2017 arsenal. Félix’s survival skills are all the more impressive when we consider that hard throwers tend to suffer disproportionate performance declines when they lose fastball speed, perhaps in part because pitchers with great fastballs can rely on their heat rather than developing deep arsenals. Félix has never suffered from a limited repertoire: He’s thrown five pitch types at least 5 percent of the time each in every season of the PITCHf/x era.

Over time, pitchers tend to throw fewer four-seam fastballs and more of almost everything else, as this pitch-type usage aging curve provided by FanGraphs’ Jeff Zimmerman reveals. (Like all aging curves that use the “delta method,” this graph is subject to some survivorship bias, but the trend is pretty plain.)

Félix has followed that trend, going away from his fastball as it’s gone away from him. In 2008, the first year for which we have complete PITCHf/x data, Félix threw four-seamers and sinkers 66 percent of the time. Over the past three years, that combined percentage has sat in the low-to-mid 40s. In 2014, the new look was working: Analysts praised Félix for mixing in more off-speed stuff and throwing low and away. Last year, it wasn’t working: He was still mixing in off-speed stuff, but those pitches weren’t getting swings, and he probably grew too accustomed to staying away from the strike zone. “He didn’t throw in very often,” Dipoto said. “He didn’t elevate very often. He stayed mostly in the same zone all year long. And if you do the same thing to major league hitters, over and over, they will sniff you out.” We can clearly see that progression in heat maps of Félix’s pitch locations to right-handed hitters in 2008, when he boldly poured pitches over the plate …

… to 2014, when he looked lower …

… to 2016, when, perhaps, reduced trust in his stuff made him more predictable and exploitable.

Over the past season and a half, we saw Tigers ace Justin Verlander go back to being a guy we could describe as “Tigers ace Justin Verlander,” after a two-and-a-half season span in which he seemed to be in the same spiral as Félix, dropping velocity and watching his ERA rise. Finally free of lingering physical concerns, Verlander smoothed out his mechanics, and his velocity climbed part of the way back to its peak. But he also adjusted, throwing his fastball up in the zone to take advantage of its high spin rate and adding some juice to his slider, which he began to throw harder and more frequently than ever before.

Stronger legs could serve as a springboard for Félix to repair his release points and find his own adjustments: more varied locations, maybe, or an even greater dependence on his changeup, which is still a shutdown pitch. Verlander is an exception with his own set of skills, so fixing Félix isn’t as simple as saying “do what Verlander did.” But if latter-day Verlander and CC Sabathia can become contact managers to make up for reduced dominance, we can still talk ourselves into Félix being a few tweaks (and a winter’s worth of training) away from a productive plateau.

The Mariners’ rebuilt rotation has a range of outcomes as wide as any starting staff’s aside from the Mets’ or the Diamondbacks’. Even their Opening Day starter (for the ninth consecutive season) could be either an ace or an albatross: Despite his accomplished past, Hernández’s future is as tantalizing and uncertain as James Paxton’s or Drew Smyly’s.

Félix is already infamous as the best player in decades who’s never appeared in the playoffs. Until at least 2016, his innings alone couldn’t change that, because the Mariners couldn’t come close enough for his contributions to count. But Dipoto has done enough that to end their October exile, the Mariners (and Félix) might only need to rediscover some semblance of the star they always could count on before.

Thanks to Jeff Zimmerman of FanGraphs for research assistance.