With Jean Segura-Taijuan Walker trade, the Mariners and Diamondbacks each try to get better

When two (or more) baseball teams make a trade, it’s common for them to deal from a strength to improve a weakness. Take last week’s Yankees-Astros swap, in which New York sent Brian McCann to Houston to free up playing time for late-season phenom Gary Sanchez. McCann has a bloated contract, but he still mans his position well, and thus the ‘Stros considered him worth swinging for. Aside from salary dumps, most trades will involve an established, reliable major-league player.

It’s far less common, though, for a team to trade away a competent major leaguer — and get back competent major leaguers — when it wants to contend. More often, one side of the transaction will receive some number of unproven young players in return. In that McCann deal, New York received two Houston prospects, neither of whom has played above Single-A ball. After pilfering the Cubs and Indians over the summer, the Yankees have decided to build for the future, and McCann may not be the last veteran to head out. Such is the nature of most trades: The contenders deal for major-league players, while rebuilders send them away.

This is what makes yesterday’s Diamondbacks-Mariners trade so fascinating. Neither of these teams met expectations in 2016, although they certainly didn’t have analogous performances — the Mariners went 86-76 and finished three games out of the AL wild card, whereas the Diamondbacks imploded en route to a 69-93 record. But each team has a formidable nucleus of talent that could translate to a playoff run, and with this trade, they’ve both improved their odds of that for 2017.

First, the specifics:

Arizona gets:

• SP Taijuan Walker
• IF Ketel Marte

Seattle gets:

• IF Jean Segura
• OF Mitch Haniger
• RP Zac Curtis

The headlining players — i.e., the ones in the headline of this article — address a position of major need for each team. By ERA-, the Diamondbacks had the third-worst rotation in baseball this season; only the lowly Twins and Athletics fared worse. Meanwhile, Mariners shortstops were the second-worst in the majors according to fWAR, as the Alexei Ramirez-led Padres kept them out of the cellar.

Into the former hole steps Walker, a 24-year-old righty with two complete seasons under his belt. While he’s notched a pedestrian 107 ERA- and FIP- to this point in his career, Walker hasn’t lost his explosive potential — he combines a mid-90s fastball with a devastating curveball-splitter one-two punch. His 15.6 percent K-BB rate over the past two years puts him ahead of Jose Quintana and John Lackey, hinting at the caliber of hurler he could grow into.

How will Walker handle the transition? Safeco Field doesn’t inflate offense like Chase Field does, so maybe he’ll continue to give up too many long balls and fall short of his potential. On the other hand, Walker will now work in the NL West, where the pitcher bats ninth and the Padres run out an all-pitcher lineup. The park factors and quality of opponents will likely cancel each other out, setting Walker’s probable floor at “back-end starter,” and his ceiling at “ace.”

Their 93 losses shouldn’t take away from the solid core the Diamondbacks have established. As SB Nation MLB’s Grant Brisbee laid out yesterday — great timing on that, Grant — the Diamondbacks still have the pieces to contend. Full seasons from Paul Goldschmidt and A.J. Pollock would give them two of the best position players in the majors. If Zack Greinke can stay healthy, Shelby Miller and Patrick Corbin can right heir respective ships, Robbie Ray can stop underperforming his FIP, and Walker can put it all together, suddenly they have a top-tier rotation as well. These hypotheticals may not all come to pass, but it looks as though the Diamondbacks will be betting they might.

And into the latter hole steps Segura, a 26-year-old infielder who’s been around since 2012. Now with his fourth organization — the Angels signed him as an international free agent, then sent him to the Brewers, who sent him to the Diamondbacks — Segura’s had an up-and-down career thus far. Like, this kind of up-and-down:

Segura was pretty much the only Diamondback unfazed by Murphy’s Law in 2016. He altered his batting stance, made progress on his plate discipline, and thereby became a 5.0-fWAR player. Depending on which metric you use, he’s either a subpar defender or a spectacular one. Even if you take the under on his glove, he should still play a competent shortstop and earn at least three wins next season.

The Mariners fared far better than the Diamondbacks this year, with Kyle Seager, Robinson Cano, and Nelson Cruz continuing to shine. Adding Segura to that mix gives Seattle an impressive position-player quadrumvirate, in addition to sealing up one of 2016’s most egregious black holes. Although the Mariners still have some uncertainty in their rotation — which dealing away Walker hasn’t alleviated — the hitters should make the team a power in the AL West.

Neither Walker nor Segura is an especially illustrious player. The former, as noted, has yet to live up to his billing, with his tantalizing hot streaks giving way to periods of ineptitude. And although the latter dominated in 2016, he really struggled in 2014 and 2015, earning a combined 0.3 fWAR in those two years. Yet each will patch up a major leak on his new team, and each could plausibly play in October next year — and play a key role in getting his club there.

Walker and Segura aren’t the only two players to switch employers in this trade. Haniger’s a 25-year-old outfielder who exploded in 2016, clubbing .321/.419/.581 across 548 plate appearances in Double and Triple A. Curtis is a 24-year-old relief prospect whose mediocre results (a 3.90 ERA in 30.0 innings this year) belie some superb peripherals (52 strikeouts and 11 walks in those 30.0 innings). And Marte’s a 23-year-old shortstop with a ton of defensive upside and a bat that could come around someday.

In a typical trade, these would be the central players heading in one direction — the contending team would bring in a major leaguer, and the rebuilding one would snatch some toolsy farmhands in return. This isn’t a typical trade, though: Neither the Diamondbacks nor the Mariners want to punt on 2017, so each of them addressed an area of need and dealt from a relative strength.

File this in with the Prince Fielder-Ian Kinsler deal from 2013 and the Rick Porcello-Yoenis Cespedes swap from 2014, as a mutually beneficial agreement between two aggressive clubs. If Walker finally breaks out and Segura doesn’t regress, no one involved will regret this trade — a rarity in today’s MLB.