Reason for optimism: Seattle discovered the joys of offense last season, and this offseason, the Mariners added a guy who outslugged Paul Goldschmidt last season.
Reason for pessimism: The addition comes at the cost of up to 30 starts from Yovani Gallardo.
The Mariners increased their run production by 112 runs from 2015 to 2016, and close to half of that increase came from the easiest source of improvement a team will likely ever have. By replacing their 2015 catchers, who collectively hit worse than at least one National League pitching staff in 2015, with nearly exactly league-average catcher production, the Mariners gained roughly 50 runs last season.
The other 70 runs of marginal improvement partially came from yet another career year from Kyle Seager, who has seen his home runs increase every season since his debut in 2011, and a spectacular year from Robinson Cano, who hit more home runs last year (39) than he did in his first two seasons with Seattle (35).
Perhaps sensing that production from a career year is prone to regress the next year, as well as wondering how many 40-home-run seasons 36-year-old Nelson Cruz can possibly have left in him, the Mariners' front office pulled the one easy-to-reach lever they had to improve the offense just a bit more in an effort to finally get to the postseason in the Felix Hernandez era. They replaced their least-productive offensive player, shortstop Ketel Marte (.259/.287/.323), in a trade with Arizona that landed Jean Segura (.319/.368/.499) in return.
There are markers in Segura's production, in addition to his previous 2,000 plate appearances, that suggest his 2016 isn't repeatable. In fact, his 2015 season in Milwaukee (.257/.281/.336) looks remarkably like Marte's season last year. Seattle almost certainly thinks it has found the source of 30 to 40 more runs, which might get the team to 90 wins, but I highly doubt it.
Whether or not I'm right about the offense, there's a very good chance that the trade is going to hurt the Mariners on the runs allowed side of the ledger.
Seattle not only shipped Marte to Arizona but also had to part with Taijuan Walker. Now, Walker was just a mildly above-average starter last year, with a 4.22 ERA in an American League in which starters posted a 4.42 ERA as a whole. The problem is that Seattle signed Gallardo as a free-agent over the winter, and he had a 5.42 ERA last season. ERAs of 5.00-plus aren't unheard of because of bad luck or bad defense, etc., but according to SIERA, which measures a pitcher's skill set, Gallardo deserved every bit of his ERA. His SIERA of 5.34 stood third-worst in all of baseball among starters who threw at least 100 innings.
While their other addition to the rotation, Drew Smyly, had a 4.88 ERA last season, there's a good bit of evidence that he is a better pitcher than that, so perhaps some runs allowed gains will be realized in replacing Wade Miley's 19 starts last season. New faces aside, though, there's an elephant in Seattle's rotation, and even fans of the team know it.
Hernandez posted a 3.82 ERA last season, and though that's much higher than his career mark of 3.16, it still qualifies a pitcher as quite effective. Underneath the veneer of effectiveness, though, lies an ugly truth: Hernandez's skill set is rapidly falling apart. He struck out just 18.6 percent of the batters he faced, which is solidly below the MLB average of 20.2 percent. At the same time, his walk rate hit a career low of 9.9 percent, a shocking 2.2 percent higher than that of an average MLB starter.
As a baseball fan who has loved watching the King pitch for more than a decade, it's awful to say, but it happened to CC Sabathia, it happened to Tim Lincecum and it happened to Roy Halladay, former Cy Young Award winners all. It sure looks like Hernandez might have a 5.00 ERA season in his near future.
Seattle wasn't quite as good as last year's 87 wins suggested; I graded the Mariners as an 84-win team. Additionally, it didn't seem to get any attention, but Seattle wrested away from the Yankees a distinction New York has held for many, many years: They fielded the oldest lineup in baseball. My model does not like the combination of career years in 2016 and the effects of age on regression and defense. It sees all sorts of problems for the rotation as well, and with the total wins market having opened at 85.5, this is a high-conviction "under" call.
2017 projection: 81-81 (third in the AL West)
Bet recommendation: Under