By Cliff Corcoran
June 04, 2014

Marcus Stroman (Tom Szczerbowski/Getty Images)Marcus Stroman shone in his first MLB start, striking out six in six innings. (Tom Szczerbowski/Getty Images)

The prospects are coming. With the vague Super Two arbitration eligibility cutoff due to pass soon, a good number of the game's top prospects should be called up to the majors in the coming weeks. Already, we've seen two of the minors' best hitters debut and make immediate impacts in their very first games. With that in mind, here is our prediction as to which of this year's midseason call-ups will have the biggest impact on their teams.

1. Gregory Polanco, RF, Pirates

Polanco made headlines in early May by declining a seven-year, $25 million extension from the Pirates that would have enabled the team to promote him to the major leagues without concern about his arbitration eligibility. As a result, he has remained in Triple-A, where he has continued to rake, hitting .305/.373/.476 since news of the extension offer broke on May 7. However, with the estimated Super Two cutoff approaching, the Pirates having won 11 of their last 16 games, and the team's rightfielders having hit a mere .257/.313/.350 on the season, Polanco's promotion may finally be imminent. SB Nation's Chris Cotillo reported on Monday that Polanco is expected to be called up during the Pirates' upcoming homestand, which starts on Friday.

The 22-year-old Polanco is a five-tool talent with developing power, impact speed on the bases, a strong arm, and enough range afield to give the Pirates an outfield comprised of three men capable of playing center. Imagine the Pirates adding another Starling Marte for right field, but younger and more productive at the plate and on the bases, and you'll get the gist. Heading into Wednesday's action, the Pirates are just two games behind the National League wild-card leaders. Don't be surprised if the addition of Polanco puts them back in the playoff hunt to stay.

2. Jonathan Singleton, 1B, Astros

By accepting the sort of extension that Polanco and teammate George Springer declined, Singleton has one thing few players in their first week in the major leagues can claim: Financial security. His new five-year, $10 million contract also gives him a measure of job security, as the Astros' lowly position in the standings and investment in Singleton give them little reason to overreact to an early slump. By that measure, Singleton, despite some of the negative attention his extension has drawn, is perhaps facing less pressure than the typical player in his position. That could ease his transition to the major leagues, which began Wednesday night when Singlteon walked and homered in the Astros' win over the Angels.

Singleton also struck out twice and made two errors, but he's replacing an assortment of Astros first basemen who hit .181/.269/.291 prior to his arrival. Given that, Singleton could have a significant impact simply by bringing the team's performance at the position up to replacement level. Of course, we expect far more than that from a 22-year-old who hit .267/.397/.544 in Triple-A before his promotion and has now hit 15 home runs in 243 plate appearances on the season.

3. Marcus Stroman, RHP, Blue Jays

Stroman spent two weeks in the Blue Jays' bullpen in early May, but he's a starting pitcher and was just recalled to join the Toronto rotation on Saturday, so he still counts as a midseason call-up in our book. The bar for Stroman's achievement is almost as low as Singleton's, as the Blue Jays have struggled to fill the back of their rotation. Brandon Morrow is out until at least the All-Star break with a torn tendon sheath in his pitching hand, Dustin McGowan was bounced to the bullpen in mid-May after posting a 5.08 ERA in eight starts, and J.A. Happ has alternated good and bad outings to the tune of a 4.09 ERA since returning to the rotation as Morrow's replacement in early May.

Stroman took over the fifth spot from Liam Hendriks over the weekend and sparkled in his first major league start, holding the Royals to one run over six innings while striking out six against no walks; at the very least, he seriously impressed Kansas City first baseman Eric Hosmer. In seven Triple-A starts this season, he has posted a 3.03 ERA while striking out 45 against just nine walks in 35 2/3 innings, remarkable numbers for a right-handed pitcher who is likely shy of his listed height of 5-foot-9. Stroman has made a believer of most prospect watchers, however, with his mid-90s heat, deep repertoire (cutter, sinker, change, curve, and a nasty slider), excellent command and mound presence. If Stroman can pitch up to his potential over the remainder of the season, he could help keep the Blue Jays atop the American League East standings. The only catch is that both he and fellow 23-year-old Drew Hutchison, who is making a strong comeback from Tommy John surgery, could run into innings limits down the stretch

4. Oscar Taveras, OF, Cardinals

Taveras is widely considered the top hitting prospect in baseball and the third-best prospect in the game overall, and went deep in his second major league at-bat on Saturday. So why is he merely fourth on this list? Because the Cardinals are so stocked with talent it's not entirely clear where he'll play once Matt Adams returns from the disabled list, or if the 21-year-old Taveras will even remain in the majors past that point (he's just 2-for-11 since the home run without another extra-base hit, and a demotion could negate his potential Super Two status). Centerfield seems like the most likely place for Taveras on a healthy Cardinals team, though he could also fall into a fourth-outfielder role that finds him starting two-thirds of the team's games without a set position. If he replicates his minor league rates (.321/.377/.519 with a similar line in 49 games at Triple-A this season), he'll be an upgrade no matter where or how the Cardinals use him, but his play in center (he's not considered a long-term option at the position) could undermine his production, and his lack of security or stability could undermine his comfort at the plate.

5. Andrew Heaney, LHP, Marlins

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