With Spring Training rapidly approaching, we're taking an in-depth look at the Mariners' roster. This is the sixth part of an Around the Horn series looking at each position on the team. Today: the outfield.
The big question: Can the young guns keep improving?
The Mariners relied heavily on rookies in the outfield in 2017, with Ben Gamel starting 127 games, Guillermo Heredia 104 and Mitch Haniger 95. In doing so, they became just the third MLB team since 1913 to have three rookie outfielders make 80-plus starts and the first since the Royals in '69.
That group proved productive as well. Haniger spent 60 days on the disabled list due to a strained oblique and lacerated lip, but he opened eyes in right field when healthy with a .282/.352/.491 slash line, 16 home runs and 47 RBIs.

Gamel was promoted from Triple-A Tacoma when Haniger went on the DL in late April and played so well that he shifted to left field upon Haniger's return and wound up slashing a solid .275/.322/.413 of his own, with 11 homers and 59 RBIs.
Heredia's numbers dropped considerably in the final six weeks when he played through a shoulder issue that eventually required surgery as the 27-year-old Cuban wound up with a .249/.315/.337 slash line, nine homers and 36 RBIs, but he was batting .286 in mid-August before tailing off.
All three return for 2018, though Heredia might not be quite ready at the start of the season as he's still recovering from his September surgery.
The starters: Haniger, Dee Gordon, Gamel
Haniger and Gamel are again penciled in right and left field, but they'll flank a new man in center as general manager Jerry Dipoto acquired the speedy Gordon from the Marlins and will move him from second base to the outfield.

Gordon led the Majors in stolen bases in three of the past four seasons, including 60 last year when he slashed .308/.341/.375 with two homers, 33 RBIs and 114 runs scored. The two-time National League All-Star will hit leadoff for Seattle and figures to provide a nice boost to a lineup that now can shift Haniger and Gamel lower in the order.
Backing up: Heredia, Cameron Perkins
Once his shoulder fully recovers, Heredia figures to handle the backup duties at all three outfield spots. He played well in center last year while sharing time with Jarrod Dyson, who is now a free agent. The Mariners consider Heredia an outstanding defender and feel his offense can be much better than his final results from last season once he's healthy.

Perkins, claimed off waivers from the Phillies in December, could have a shot at the fourth outfield spot until Heredia is ready to roll. The 27-year-old played 42 games for Philly last year, hitting .182, but he's put up good numbers in Triple-A and is on Seattle's 40-man roster.
Andrew Romine and Taylor Motter are competing for the utility role and both have enough outfield experience to fill in if needed. Romine started 44 games in the outfield last year for the Tigers, including 20 in center. Motter made 14 outfield starts for Seattle.
Depth: Kirk Nieuwenhuis, John Andreoli, Braden Bishop, Andrew Aplin, Ian Miller
Of the five non-roster invitees to camp, Nieuwenhuis is the only one with Major League experience. The 30-yearold played 414 games with the Mets, Brewers and Angels over the past six seasons with a .221/.311/.384 line, 31 homers and 117 RBIs. He made Milwaukee's Opening Day roster last year, but was 3-for-26 in 16 games and wound up spending most of the season in Triple-A.

Bishop and Miller are two youngsters getting their first invites to big league camp. Bishop, 24, is Seattle's No. 4 prospect per MLB Pipeline and an excellent defensive center fielder who put up a .306/.393/.413 line at Class A Advanced Modesto and Double-A Arkansas.
Miller, 25, is the club's No. 20 prospect and earned the Mariners' Minor League Hitter of the Year honors last year after posting a .307/.355/.393 line with 43 stolen bases at Arkansas and Tacoma.

In the pipeline:
In addition to Bishop and Miller, the Mariners have some other intriguing outfield prospects coming up. Julio Rodriguez is a lanky 17-year-old out of the Dominican Republic who is already rated their No. 5 prospect by MLB Pipeline before making his pro debut.
Luis Liberato (No. 9) is a 22-year-old Dominican who has been slowed by injuries, but advanced to Modesto last year. Anthony Jimenez (No. 10) is a 22-year-old from Venezuela who played for Class A Clinton, while Greifer Andrade (No. 11) is another Venezuelan who moved back to the outfield last season for Class A Short Season Everett, where he played alongside Ronald Rosario (No. 13), a 20-year-old from the D.R.

Eric Filia (No. 21) was one of Seattle's fastest-rising prospects as a 25-year-old out of UCLA who led the Arizona Fall League with a .408 average after batting .326 for Modesto. But he just drew an 80-game suspension for a drug of abuse and will sit out the first half of 2018.
By the numbers:
Among players with 400-plus plate appearances, Haniger had the fourth-best OPS of any rookie in the Majors at .843, behind only AL Rookie of the Year Award winner Aaron Judge of the Yankees, NL Rookie of the Year Award winner Cody Bellinger of the Dodgers and Paul DeJong of the Cardinals.