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Whether the Seattle Mariners ever win a World Series under general manager Jerry Dipoto’s stewardship is unknown. But, one thing is certain — he’s made good on his promise to improve the team’s outfield defense and athleticism.

You see, Dipoto’s predecessor — Jack Zduriencik — had developed a penchant for acquiring power-hitting outfielders during his seven-year stay in Seattle. As a result, he willingly overlooked the defensive and base running deficiencies of players who could thump the ball.

Since becoming the Mariners’ general manager in September 2015, Dipoto has taken a different approach to roster construction. In his mind, a run saved is as valuable as a run scored.

Gone are the days of adding lumbering players with limited range — Nelson Cruz, Mark Trumbo, Corey Hart, Raul Ibanez, and Michael Morse — just because they had pop in their bat. Also scrapped is the mindset that infielders such as Brad Miller, Rickie Weeks, and Ketel Marte could learn the outfield via on-the-job training at the big league level.

Still, the reshaping of Seattle’s outfield was neither quick nor easy.

Dipoto couldn’t completely refurbish his outfield in year-one without jeopardizing his club’s ability to score runs. Essentially, the 48-year-old executive had to balance the influx of more athletic — yet less established — players with the retention of proven offensive weapons.

In the end, the Mariners had their best offensive season in nearly a decade, but didn’t achieve the desired outfield improvements. To see what I mean, here’s a comparison of Zduriencik’s last year and Dipoto’s debut season in several key areas — on-base ability, outfield defense and base running proficiency.

Mariners MLB Rankings
Yr On-Base Ability Outfield Def (UZR)
Base Running
2015 22 14 25 27 18 29 23 29 29
2016 9 14 12 26 27 14 21 26 24

To compare outfield defense, I’m using a stat I haven’t previously used — ultimate zone rating (UZR). FanGraphs uses UZR to make its wins above replacement (fWAR) calculations for non-catchers.

Factors used in UZR include a defender’s arm and range, double plays made by infielders, and a comparison of errors made at the position being evaluated. If you’d like to read more about UZR, FanGraphs has a great explanation with lots of formulas and other big-brained stuff here.

The other sabermetric I’ve employed is BsR (Base Running), which is another FanGraphs statistic. BsR takes into account base running elements — such as stolen base success, taking extra bases, and being thrown out while on base — to quantify a runner’s success on the base path.

For those more inclined to use longer established statistics, I threw in stolen base percentage (SB%), which illustrates runner’s success at swiping bags.

Okay, to the table.

As evidenced by their dramatically improved on-base percentage (OBP) and strikeout rate (SO%), the Mariners were a superb offensive unit in 2016. The most telling indicator was the scoreboard — they ranked sixth in the majors in runs scored-per-game.

On the other hand, Seattle’s progress in outfield defense and base running was far less dramatic — almost negligible. In one case, their defense regressed. Some of this can be attributed to offseason acquisitions, plus the retention of several Zduriencik-era players.

Early in the season, Leonys Martin flashed more power than expected and was a superb defender in center field. But, the 28-year-old was hampered after a late-May hamstring strain. Despite the setback, Martin proved to be a considerable upgrade and now serves as the anchor in Dipoto’s revamped outfield.

Conversely, the Mariners took a step backwards in left field defense thanks to the struggles of Nori Aoki. To be fair, he wasn’t the only guilty party. Seth Smith — a below-average fielding Zduriencik holdover — actually had a worse UZR in left field than Aoki.

In right field, the trio of Smith, Cruz, and Franklin Gutierrez each played over 400 innings and predictably delivered less than optimal results, just as they did in 2015. Having said that, all three were important cogs in the Mariners’ offensive machine.

Since the end of the season, the Mariners have parted ways with Aoki, Gutierrez, and Smith. The only remaining Zduriencik outfielder is Cruz and he’s likely to serve as full-time designated hitter except when the Mariners play in National League ballparks.

Now, Seattle has a projected starting outfield of Martin, Jarrod Dyson, Mitch Haniger with Guillermo Heredia and Ben Gamel entering Spring Training as their primary backup candidates. Moreover, Boog Powell is set to start the season at Class-AAA Tacoma. Each of these players is capable of playing center field.

Seattle’s New Outfield
SLG SB UZR Rank **
Leonys Martin 576 .247 .306 .378 24 27
Jarrod Dyson 337 .278 .340 .388 30 5
Mitch Haniger 123 .229 .309 .404 0 N/A
Guillermo Heredia 107 .250 .349 .315 1 N/A
Ben Gamel * 533 .308 .365 .420 19 N/A
Boog Powell * 277 .270 .326 .359 10 N/A
  * MiLB stats    ** UZR Rank includes all MLB OFers w/750 or more innings

Granted, Martin and Dyson are a notch above the rest as center field gloves. But, the versatility Dipoto has created makes the Mariners’ outfield defense formidable and far less vulnerable to injury — unlike last season.

During Martin’s injury-related absence, manager Scott Servais primarily used Aoki in center field. While the veteran wasn’t as bad as some fans believe, he wasn’t a suitable substitute either. The Mariners’ precariously thin center field depth was exposed. That won’t happen in 2017.

While there’s a lot to like about Seattle’s new outfield, I’m not suggesting it’s the best unit in their 40-year history — hardly. The majority of the unit is unproven.

Martin and Dyson are the lone established major leaguers with the remaining cast untested. Yes, their defensive and base running skills will easily translate. But, each player must demonstrate he can hit big league pitching. Otherwise, Servais will be tending to a flock of fourth outfielders.

Eventually Powell may be another option. But, he’s still serving an 80-game suspension for performance enhancing drug use and should join the Rainiers in early April. It’s worth noting that the Mariners opted to utilize Aoki rather than promote Powell when they desperately needed a center fielder. Perhaps, that’s the best indicator of the 23-year-old’s major league readiness.

Despite the uncertainty surrounding the young players acquired by Dipoto, the evolution of the Mariners’ outfield over the last 16 months has been impressive.

Sure, the outfield plan could go sideways in 2017. But, Dipoto added a layer of offensive insurance with Danny Valencia and has repeatedly proven he’ll proactively improve his roster when needed.

Time will only tell if Dipoto’s vision leads to postseason success. But, fans should be able to find a measure of comfort in knowing that outfield run prevention once again matters to the Mariners.

That bodes well for the club’s World Series aspirations.

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