Mutt Mantle was a forward thinker, years ahead of his time. In his drive to keep his son Mickey out of the blasted mines, the Oklahoman taught him to switch-hit as soon as the kid was old enough to pick up a bat.
It worked out nicely for The Mick when he reached the big time with the Yankees, freeing him from manager Casey Stengel's trend-setting platoons. The elder Mantle understood the spin of breaking balls -- and logic. Left-handed hitters historically have an easier time picking up a right-hander's deliveries, and the same logic applies to right-handed hitters facing lefties.
While it's no big surprise that left-handed superstars Joey Votto (1.009 OPS), Bryce Harper (.986) and Anthony Rizzo (.881) mashed lefties in 2015, other lefty swingers managed to convince their managers they needed no protection from nasty southpaws. Fantasy owners might take note of these platoon-proof left-handed hitters:
Lucas Duda, Mets
Emerging as a force alongside Yoenis Cespedes in the heart of the National League champions' order, Duda crushed lefties with an OPS of .878 that was 29th highest in the Majors. He was better for average (.285 to .230) and power (.545 vs. .466 SLG) against lefties, banging seven homers in 123 at-bats vs. southpaws. There's no reason for manager Terry Collins to rest big Duda against these guys.
Colby Rasmus, Astros
Another lefty who has learned to stay in against lefties, Rasmus batted .252 with a .364 OBP and a .471 slugging rate. He slugged slightly higher (.476) against righties, but his OPS of .835 was better against lefties than his .770 versus righties. Rasmus struck out at a higher rate of 35.8 against righties.
Kyle Seager, Mariners
Seager flaunted an .835 OPS against southpaws, hitting .297 and slugging .511. The third baseman had 13 homers in 229 at-bats against lefties, 13 in 394 at-bats against righties. His OBP was slightly better (.330 vs. .324) vs. right-handers, but he hit only .249 against them. It runs in the family. Kid brother Corey, another left-handed hitter and the No. 1 MLBPipeline.com prospect, hit .325 and slugged .500 vs. lefties in September for the Dodgers.

Dee Gordon, Marlins
En route to the NL batting crown with a .333 average, the Gordon batted .350 against southpaws, .327 vs. righties. The son of Tom "Flash" Gordon, a righty with speed of another brand on the mound, the Gold Glove second baseman was better across the slash board vs. lefties. Gordon slugged .450 and reached base at a .373 clip.
Mike Moustakas, Royals
Helping drive Kansas City to its World Series title, Moustakas matched Gordon's .823 OPS against lefties, reflecting his maturity as a hitter. "Moose" had a higher slugging mark (.485 to .461) but hit for a slightly better average (.286 to .282) against righties.

Alex Gordon, Royals
Another equal-opportunity banger in manager Ned Yost's lineup, Gordon had a .280/.377/.440 slash line vs. lefties, .266/.377/.428 vs. righties. The Royals would not have been the same team if they hadn't succeeded in bringing back their brilliant left fielder.
Brock Holt and Jackie Bradley Jr., Red Sox
Blessed with rare versatility, Holt was better across the slash board against lefties (.312/.394/.413), compared to .270/.333/.368 vs. righties. Bradley, as gifted defensively as any center fielder in the game, also torched southpaws, his .306/.390/.528 line surpassing his .221/.308/.483 vs. righties.
Nori Aoki, Mariners
Like Seager, his new teammate, and his former Royals buddies, Aoki is extremely comfortably taking his swings against lefties. Aoki hit .333 with a .400 OBP vs. lefties in 2015. Only his slugging mark (.383 vs. 374) was slightly better against right-handers. This was no aberration; Aoki is a .321 career hitter vs. lefties, compared to .272 against righties.
Adrian Gonzalez, Dodgers
From his earliest days with the Padres, Gonzalez has taken lefties effectively to the opposite field. The Dodgers' anchor hit .294 against lefties and only .267 vs. righties in 2015, but 24 of his 28 homers came against right-handers. Gonzalez's .498 slugging mark eclipsed his .436 vs. lefties.