Future Stardom Fact or Fiction with MLB's 10 Biggest September Call-Ups

Back in early August we played "Future Stardom Fact or Fiction" with this year's standout rookie class, and the piece generated some good discussion and debate among readers.

Now that rosters have expanded and several more highly regarded prospects have made their way to the majors, let's revisit that idea with this year's 10 biggest September call-ups.

First, we need to establish what it means to be a star player.

For the sake of this article, a "star" player is considered someone who is consistently among the best in the league at his respective position and one of the primary producers for his respective team.

Minor league track record, physical tools and and long-term profile all played a part in predicting a player's future standing.

Who among this year's wave of September call-ups will be starring in this league in the near future? Let's find out.

2B Javier Baez, Chicago Cubs

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Future Star: Fact

2015 Stats

• MiLB: 293 AB, .328/.391/.526, 15 2B, 13 HR, 62 RBI, 52 R, 18 SB
• MLB: 17 AB, .235/.316/.412, 0 2B, 1 HR, 3 RBI, 1 R, 0 SB

Player Outlook

The past two years have been a roller coaster for Javier Baez, and this year in particular has been an incredibly tough one for him between the death of his sister and a broken finger right when he was on the cusp of returning to the majors.

Kevin Van Valkenburg of ESPN.com wrote a great piece on the full Baez story that's worth a read if you're not familiar with all the ups and downs he's had to endure of late.

At any rate, Baez returned from the finger injury on July 23 after missing nearly two months and went on to hit .340/.396/.516 with eight doubles, five home runs and 33 RBI in 37 games leading up to his promotion on Sept. 1.

After Baez struck out at a dizzying 41.5 percent clip in 213 at-bats down the stretch with the big league club last season, understandable concerns popped up surrounding his ability to make enough contact to ever tap into his immense power potential.

He's always going to strike out, but he lowered that rate to a more reasonable 24.3 percent in Triple-A this year, and that included a 21.2 percent rate after he returned from the broken finger.

There's no reason to think he can't be the team's everyday second baseman by next season. If he can keep the strikeouts under control, he could immediately pass the Minnesota Twins' Brian Dozier as the top power threat at the position.

RHP Miguel Castro, Colorado Rockies

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Future Star: Fiction

2015 Stats

• MiLB: 3-3, 2.82 ERA, 1.357 WHIP, 20 BB, 38 K, 38.1 IP
• MLB: 0-3, 6.14 ERA, 1.773 WHIP, 8 BB, 12 K, 14.2 IP

Player Outlook

The continued progression of Jeff Hoffman will likely be the deciding factor in whether the Colorado Rockies come out on top in the Troy Tulowitzki deal, but don't discount the potential contributions of another right-hander, Miguel Castro.

Still just 20 years old, Castro broke camp as part of the Toronto Blue Jays bullpen, despite never pitching above the High-A level prior to this season.

He began the year with a 1.04 ERA and three saves in four chances over his first eight appearances but hit a rough patch from there; he was back in the minors by May 4.

There's a good chance the big, 6'5" right-hander still winds up in the rotation long-term, and the Rockies will no doubt give him every chance to start given their perpetual need for rotation help.

He was 8-3 with a 2.67 ERA, 1.017 WHIP and 76 strikeouts in 77.2 innings as a starter in 2014, and while his ceiling is likely that of a No. 3 starter, that could still make him a key piece of the Rockies future.

RHP Zach Davies, Milwaukee Brewers

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Future Star: Fiction

2015 Stats

• MiLB: 6-8, 3.30 ERA, 1.356 WHIP, 45 BB, 102 K, 128.1 IP
• MLB: 1-0, 3.97 ERA, 0.971 WHIP, 3 BB, 7 K, 11.1 IP

Player Outlook

The Baltimore Orioles drafted Zach Davies out of high school in the 26th round in 2011 but traded him to the Milwaukee Brewers at the 2015 deadline in exchange for outfielder Gerardo Parra.

Davies' fastball doesn't light up the radar gun, but he commands it well and pairs it with what might be the best changeup in minor league baseball and a curveball that gives him a third plus offering.

It didn't take the Brewers long to see what they had in the 22-year-old right-hander, as they made him a September call-up and immediately inserted him in the starting rotation.

His first two starts went as follows:

• Sept. 2: ND, 4.1 IP, 4 H, 4 ER, 3 BB, 3 K
• Sept. 7: W, 7.0 IP, 4 H, 1 ER, 0 BB, 4 K

That first win Monday was an impressive one, as he needed just 92 pitches to get through seven innings and didn't walk a batter. A few more starts like that and he'll be well on his way to winning a rotation spot in 2016.

"Davies' ceiling is obviously limited, but it's becoming more and more apparent that he has a good chance of reaching his upside as a No. 4 or 5 starter in the near future," wrote MLB.com's Prospect Watch.

For an outfielder set to hit free agency in Parra, a solid back-of-the-rotation starter with age on his side and a high floor is a solid return.

RHP Carl Edwards Jr., Chicago Cubs

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Future Star: Fiction

2015 Stats

• MiLB: 5-3, 2.77 ERA, 1.211 WHIP, 41 BB, 75 K, 55.1 IP
• MLB: 0-0, 0.00 ERA, 1.000 WHIP, 1 BB, 0 K, 1.0 IP

Player Outlook

The Chicago Cubs acquired Carl Edwards Jr. from the Texas Rangers in the deal that also brought in Neil Ramirez and Justin Grimm in exchange for Matt Garza. Edwards joined those two in the big league bullpen when rosters expanded.

A 48th-round pick in 2011, Edwards broke out in a big way in 2013 when he went 8-2 with a 1.86 ERA, 1.006 WHIP and 155 strikeouts in 116.1 innings.

He put up stellar numbers again last season, yet questions remained about whether his 170-pound frame would be better suited for a relief role long-term.

The Cubs moved him to the bullpen this season in an effort to expedite his arrival in the majors, but a 6.7 BB/9 rate was enough reason for pause that his promotion didn't come until rosters expanded.

Edwards is the kind of player who could take a huge step forward if his command improves, as he has electric stuff.

Until that happens, though, he looks more like a late-inning reliever and it's a transition he's taken in stride.

"I had to change my expectations from me being a starter to me being a reliever," Edwards told Carrie Muscat of MLB.com. "I can truly say I've accomplished getting here, like I said I wanted to do. No matter how I got here, as long as I got here, to help the team win, that's the big thing."

3B Joey Gallo, Texas Rangers

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Future Star: Fiction

2015 Stats

• MiLB: 321 AB, .240/.342/.520, 19 2B, 23 HR, 63 RBI, 41 R, 2 SB
• MLB: 94 AB, .202/.292/.415, 3 2B, 5 HR, 13 RBI, 14 R, 2 SB

Player Outlook

There's no question Joey Gallo has some of the best raw power in all of baseball.

When he hit five home runs during a 25-game call-up earlier this season, they traveled 430, 439, 471, 423 and 439 feet, respectively, according to the ESPN Home Run Tracker.

However, he also struck out 43 times in 87 at-bats during that brief cup of coffee, and therein lies the problem with the 21-year-old slugger.

While struggles like that are to be expected when a player gets his first taste of the majors, his 37.2 percent strikeout rate in the minors this year is far more concerning.

All told, Gallo has struck out 34.7 percent of the time during his four minor league seasons.

For the sake of comparison, Adam Dunn—who struck out a whopping 2,379 times in his career—whiffed only 18.2 percent of the time when he was coming up through the minors.

While there's no rush to thrust Gallo into an everyday role with Adrian Beltre still under contract through next season, he would ideally take a step forward and be able to step in as the starting third baseman in 2017.

For now, Gallo looks more like a Mark Reynolds-type player than a legitimate star.

RHP Frankie Montas, Chicago White Sox

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Future Star: Fact

2015 Stats

• MiLB: 5-5, 2.97 ERA, 1.223 WHIP, 48 BB, 108 K, 112.0 IP
• MLB: 0-0, 0.00 ERA, 0.000 WHIP, 0 BB, 1 K, 1.0 IP

Player Outlook

Originally signed by the Boston Red Sox, Frankie Montas came to the Chicago White Sox in the three-team deadline deal that sent Jake Peavy to Boston, Jose Iglesias to Detroit and also brought Avisail Garcia to Chicago in 2013.

After pitching to a 5.43 ERA at the Single-A level in 2013, he opened 2014 as the No. 29 prospect in the White Sox system, according to the Baseball America Prospect Handbook.

Suffice it to say he was well off the top-prospect radar, but that would change by season's end.

Over 15 starts and 81 innings of work, Montas went 5-0 with a 1.44 ERA, 0.914 WHIP and 80 strikeouts, in the process climbing to the No. 5 spot among White Sox prospects heading into this year.

With a fastball that can touch triple digits and a biting slider that sits in the high 80s, Montas has two plus pitches right now. It will be the development of his changeup that eventually determines if he's a front-line starter or a dangerous bullpen arm.

Still just 22 years old and with his stock rising so quickly in the past year, all signs point to front-line starter right now, as he could join Chris Sale and Carlos Rodon to form a lights-out trio on the South Side in the very near future.

3B Hector Olivera, Atlanta Braves

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Future Star: Fact

2015 Stats

• MiLB: 125 AB, .272/.326/.376, 5 2B, 2 HR, 10 RBI, 18 R, 0 SB
• MLB: 20 AB, .200/.238/.400, 1 2B, 1 HR, 7 RBI, 1 R, 0 SB

Player Outlook

The Los Angeles Dodgers won the bidding war for Hector Olivera this past offseason, eventually signing the Cuban defector to a six-year, $62.5 million deal that included a $28 million signing bonus.

Despite that investment, he would never play a game for the Dodgers, as he began his pro career in the minors on June 3 but wound up being traded to the Atlanta Braves at the trade deadline in a three-team, 13-player blockbuster.

After rehabbing a hamstring injury, he finally made his big league debut on Sept. 1 and will presumably serve as the Braves' starting third baseman the rest of the way.

He got off to a relatively slow start at 2-for-15 with five strikeouts in his first five games, but he broke out Monday with a 2-for-5 performance that included a double, a home run and four RBI.

At 30 years old, Olivera doesn't have the same upside and future profile of the rest of the players on this list, but he's also more polished at this point and is capable of being one of the breakout players of 2016.

"This guy was not only traded in the middle of the season, but he came from a different country and is trying to get used to the language and all of that," Braves manager Fredi Gonzalez told Mark Bowman of MLB.com. "It's going to take him a while. We have to be patient with him. But you saw what our scouts have seen, some power."

The Braves need someone to help Freddie Freeman shoulder some of the run-production load, and it wouldn't be the least bit surprising to see Olivera penciled into the cleanup spot next year.

CF Dalton Pompey, Toronto Blue Jays

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Future Star: Fiction

2015 Stats

• MiLB: 387 AB, .307/.383/.421, 9 2B, 7 HR, 40 RBI, 70 R, 23 SB
• MLB: 83 AB, .193/.264/.337, 6 2B, 2 HR, 6 RBI, 11 R, 4 SB

Player Outlook

Dalton Pompey opened 2015 as the Toronto Blue Jays' starting center fielder following the departure of Colby Rasmus, but after he hit just .193/.264/.337 in 23 games, Toronto shipped him back to Double-A to work out the kinks.

Looking back, Pompey began the 2014 season at the High-A level and ranked as the No. 17 prospect in the Toronto Blue Jays organization, according to the Baseball America Prospect Handbook.

By season's end he was one of the breakout prospects of the year, as he hit .317/.392/.469 and stole 51 bases over three levels of the minors before capping things off with a September call-up.

The emergence of defensive standout Kevin Pillar in center field this season has complicated things going forward for Pompey, but he still has the tools to be an impact table-setter and an everyday center fielder.

Until he establishes himself at the big league level, though, it's hard not to see the potential for him to be the next Anthony Gose or Travis Snider.

He's still just 22 years old, so there's plenty of time for him to take the next step, but for now we'll go with "fiction" as far as his potential for future stardom is concerned.

2B Rob Refsnyder, New York Yankees

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Future Star: Fiction

2015 Stats

• MiLB: 450 AB, .271/.359/.402, 28 2B, 9 HR, 56 RBI, 66 R, 12 SB
• MLB: 12 AB, .167/.167/.417, 0 2B, 1 HR, 2 RBI, 1 R, 0 SB

Player Outlook

The New York Yankees' decision to re-sign Stephen Drew provided a temporary roadblock for Rob Refsnyder this season, but the 24-year-old is still viewed as the future at the position.

Refsnyder hit .318/.387/.497 with 38 doubles, 14 home runs, 63 RBI and 82 runs scored in 2014, splitting the season between Double-A and Triple-A in his first taste of the high minors.

Despite those numbers, the team opted to go the veteran route, and Refsnyder has spent the bulk of 2015 back in Triple-A as a result.

With a plus hit tool and decent pop, Refsnyder has a chance to be a .280-.300 hitter with 30 doubles and 10 home runs once he establishes himself at the big league level.

That may not be star-caliber production, but it would be good enough for him to be considered an above-average producer at the second base position.

There is a lot of homegrown talent closing in on reaching the majors for the Yankees, and Refsnyder has a chance to be a significant part of what could be a future youth movement of sorts.

SS Corey Seager, Los Angeles Dodgers

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Future Star: Fact

2015 Stats

• MiLB: 501 AB, .293/.344/.487, 37 2B, 18 HR, 76 RBI, 81 R, 4 SB
• MLB: 18 AB, .333/.400/.500, 3 2B, 0 HR, 3 RBI, 4 R, 1 SB

Player Outlook

Easily the top prospect promoted in September, Corey Seager followed a similar path to Joc Pederson, who put up huge numbers in Triple-A last season but didn't receive the call to join the Los Angeles Dodgers until rosters expanded.

Baseball America ranked Seager as the No. 1 prospect in all of baseball when it updated its rankings at midseason, and he has all the tools to be a star at the shortstop position.

"Seager has a smooth, balanced lefty swing as well as bat speed, strength and a mature all-fields approach. He can get a bit aggressive at times but has what it takes to hit for both average and power," wrote MLB.com, which currently ranks him No. 2 among all prospects behind only Byron Buxton of the Twins.

Whether or not he manages to steal playing time down the stretch this year, all signs point to Seager taking over as the everyday shortstop next season after Jimmy Rollins departs in free agency.

He'll no doubt open next season as the NL Rookie of the Year front-runner, and it may not be long before he's a perennial All-Star and the latest homegrown star for the Dodgers.

All stats courtesy of Baseball-Reference and FanGraphs unless otherwise noted.