Jay Jaffe, Special to ESPN.com 5y

Prospects ready to help their teams win now

MLB, Milwaukee Brewers, Tampa Bay Rays, Oakland Athletics, Atlanta Braves, Colorado Rockies, Cincinnati Reds, Houston Astros, San Diego Padres

As a 23-year-old third baseman light on defensive skill and coming off an 80-game suspension for performance-enhancing drugs, Michael Chavis didn't figure heavily in the Boston Red Sox's preseason plans. But desperation -- and the trend toward de-emphasizing infield defense in an age of perpetually rising strikeout rates and analytically assisted positioning -- led them to try the 5-foot-10, 216-pound fireplug at second base when they recalled him in late April. The defending world champions were just 6-13 at the time, and for the second year in a row had a Dustin Pedroia-sized hole at second base. The replacements they could muster were hitting .136/.186/.152. Boston plugged Chavis into that hole, and all he has done since is rank second on the team in slugging percentage (.558) while the Red Sox have gone 20-10.

That kind of impact is something a contender can only hope for when calling up a youngster. Even the best prospect might falter in his first taste of big league action, or take time to find his footing -- far more than the two weeks it took Vladimir Guerrero Jr., sometimes. The 20-year-old consensus No. 1 prospect hit just .146/.222/.171 without a homer through his first 11 games, then .370/.469/.852 with four homers in his next eight.

Guerrero's Toronto Blue Jays don't figure to contend for a playoff spot. What follows here are eight rookies -- some of whom have only just recently arrived, or seen limited MLB action, while others have yet to be called up -- who could play a significant part in their teams' push for a postseason berth. Note that I'm not covering Rookie of the Year candidates who have been around since Opening Day, such as the Mets' Pete Alonso or the Padres' Chris Paddack -- though bless their respective teams for not gaming their service-time clocks -- nor is the primary concern here long-term potential (that's what top-100 lists are for).

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