Kyle Schwarber, Carlos Correa and Trea Turner each came up from the minors before the All-Star break and had a strong second half to catapult their teams into the postseason over the past two years.
Which rookies can make the biggest impact down the stretch this year?
Aaron Judge, Cody Bellinger, Andrew Benintendi, Trey Mancini and Yuli Gurriel are excluded from this list because they've been in the majors since April.
Here are five potential difference-makers who were called up after May 1:
Clint Frazier, New York Yankees, OF: Frazier is batting .292 (7 for 24) with six extra-base hits, including three homers, since being called up July 1 following a rash of injuries in the Bronx. Acquired last July in the trade that sent reliever Andrew Miller to Cleveland, Frazier made news in spring training because he was reluctant to cut his long red curls. Now, New York's top prospect is making headlines for his performance. If Frazier returns to Triple-A when Matt Holliday comes off the disabled list, it won't be long before he's back in the majors. The Yankees are 3½ games behind first-place Boston in the AL East and tied atop the wild-card standings. Frazier could give the lineup an extra boost in September.
Ian Happ, Chicago Cubs, 2B/OF: Happ came up to the majors on May 13, less than two years after he was selected with the ninth overall pick in the first round. He's been so impressive for the defending World Series champions that manager Joe Maddon has not only kept him in the lineup but batted him cleanup over the weekend behind reigning NL MVP Kris Bryant and Anthony Rizzo. Happ is hitting .257 with 13 homers and 31 RBIs in only 183 at-bats. The Cubs are 5½ games behind NL Central-leading Milwaukee and Happ's big bat could carry them in the second half.
Bradley Zimmer, Cleveland Indians, CF: Zimmer was recalled May 16 after the Indians placed a third outfielder on the disabled list and the 2014 first-round pick is here to stay. Zimmer is batting .285 with five homers, 25 RBIs and nine steals in 49 games. The Indians are 27-22 since his arrival and lead the AL Central by 2½ games over Minnesota. Zimmer can be key role in helping Cleveland repeat as AL champs.
Paul DeJong, St. Louis Cardinals, 2B/SS: DeJong finished off an impressive six-week stretch with a record-setting performance over the weekend. He had seven extra-base hits against the Mets, becoming the first rookie since 1900 with more than six in a series. DeJong is batting .313 with nine homers and 20 RBIs in 36 games since his debut on May 28. The Cardinals are 5½ games behind the Brewers in the NL Central. DeJong, who came up when Kolten Wong was injured, has helped them stay in contention in a mediocre division. A strong second half could get St. Louis over the top.
Jacob Faria, Tampa Bay Rays, P: Faria has been outstanding for the Rays since coming up June 7, going 4-0 with a 2.11 ERA in six starts. The right-hander has been an excellent addition to a solid rotation and he's helped Tampa stay in the mix in the AL East. The Rays are tied with the Yankees, 3½ games behind Boston. Faria has delivered six quality starts, giving the Rays a chance to win every fifth day. If he continues pitching this well, he could take the mound in October.