Late summer has seen a number of young players disrupt fantasy pennant races with short samples of elite production. But are these baby-faced assets the real deal?

On this week’s Regression Report, let’s look at five young hitters who have exceeded expectations over the last month and who therefore top the ESPN most-added list. Is this production sustainable? Are these worthy fantasy starters for the stretch run?

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Byron Buxton (OF – MIN)
Ownership up 33% in ESPN leagues

For the second season in a row, Twins youngster Byron Buxton is complicating his value by following a long stretch of early-season futility (.604 OPS and 31% strikeout rate over 286 first-half PAs) with a hot late summer surge, tallying a .964 OPS across his last 82 PAs while cutting his strikeout rate below 26%.

It’s not as if Buxton is smoking the ball in the recent sample. His hard-hit rate in the recent sample is just over 30%, a small improvement on the 26% rate we saw in the first half. The difference is the major improvement in soft-contact, over 22% before the All Star break and now just 8% over the last month.

The preponderance of what is categorized as “medium” contact (61%) in the recent sample has allowed Buxton to turn his speed into a difference-making quality, helping Buxton to a .408 BABIP over the last month, a hundred-point boost on the first-half sample.

There’s no doubt that with his game-changing speed, Buxton can maintain a BABIP somewhere near the high .300s. The question is whether his issues with making contact will prohibit his opportunities to show off that speed. Buxton’s 35% reach rate shows he’s still a rather undisciplined hitter at times, and his low 68% swing rate at strikes seems to indicate that he still has trouble understanding the zone.

Buxton’s upside makes him a super appealing asset for the home stretch in 2017. As for Buxton’s stock in 2018 drafts, there’s a good chance his cost will once again fail to account for his wide range of possible outcomes.

Eddie Rosario (OF – MIN) 
Ownership up 24%

Buxton’s teammate, Eddie Rosario, might not have the elite prospect pedigree, but to some extent his recent success (1.012 OPS over the last month) looks even more legitimate than Buxton’s.

Rosario’s stingy 16% strikeout rate over that span is certainly a welcome alternative to Buxton’s free swinging, with Rosario’s strong strike zone awareness (75% swings at pitches in the zone) and excellent 80% contact rate providing some reassurance that his .346 BABIP on the month is more fact than fiction.

Rosario’s shrewd batting eye has allowed him to drive the ball with authority, tallying a hard-hit rate approaching 39% and a a pull rate above 43%. Owners who need average and RBI more than they need Buxton’s speed might consider Rosario a worthy add. Come 2018 drafts, Rosario might cost a heck of a lot less while offering a much higher floor.

Cory Spangenberg (2B/3B/OF – SD)
Ownership up 20%

Those who were too slow to pounce on those surging Twins outfielders might see young Padres utility man on their most-added list and wonder what all the fuss is about.

Spangenberg’s six combined homers and steals with 33 combined runs and RBI over the last month would seem to register him as a worthy flyer in mixed leagues, though it’s hard not to cast a sideways glance at that 27% HR/FB rate and wonder how likely the 26-year-old is to keep this up.

After all, Spangenberg’s career HR/FB is closer to 14%, and even that number seems like an embellishment of his mid-single digit averages in the minors. With a career hard-contact rate around 27%, Spangenberg seems like a filler asset at best. Owners shouldn’t feel remorseful about cutting him if a player with more upside touches their wire in the coming weeks.

Rhys Hoskins (1B/OF – PHI)
Ownership up 12%

Hoskins is one such player, impressing mightily in his first taste of MLB action, with a 1.015 OPS across his first 45 PAs and a walk rate (17%) that’s actually higher than his strikeout rate (just under 15%).

Indeed, Hoskins’ poise at the plate might mean that there’s some improvement coming on his .237 batting average. Sure, that 48% hard-hit rate will be hard to sustain as pitchers adjust to the young Phillie, but with a shrewd 27% reach rate and elite (albeit small-sample buoyed) 96% contact in the zone, Hoskins looks somewhere close to the real deal.

As for owners who are still competitive in standard leagues, Hoskins should be a popular mid-round flyer with massive upside come next year’s drafts.

Rafael Devers (3B – BOS)
Ownership up 12%

Arguably the most impactful of the late-summer callups, Devers is also, along with Hoskins, one whose underlying skills dispel fear that this is a sample-size aberration.

Managing a 39% hard-hit rate over his first 93 PAs, Devers has shown the ability to hit to all fields and play off Boston’s Green Monster, poking the majority of his balls (about 43%) to the opposite field.

And while it’s fair to expect Devers’ .333 batting average to fall back to earth a bit, his swinging strike rate just below 10% and contact rate above 90% suggest that a number somewhere in the .290 to .300 range isn’t an overly optimistic expectation going forward, especially considering his current 25% strikeout rate is a bit higher than the high-teens marks we saw from him in the minors.

Devers seems like a reliable fantasy starter going forward, and he should have a fair bit of helium to his draft stock going into next season.

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Tom Whalen is a featured writer at FantasyPros. For more from Tom, check out his archive or follow him @tomcwhalen.