In 2015, a handful of rookies took the league by storm. Noah Syndergaard racked up just under 10 K/9, and striking out better than five batters for every one that he walked. Roberto Osuna jumped from High-A to the back of the Blue Jays bullpen, picking up 20 saves in 23 chances, posting a 2.58 ERA along the way. Kris Bryant performed at an MVP level from wire-to-wire, while Francisco Lindor and Carlos Correa hearkened back to the heyday of Derek Jeter, Nomar Garciaparra, and Alex Rodriguez. And Miguel Sano and Kyle Schwarber flashed the sort of prodigious power that can make a grown man swoon.
Why do I bring this up? In short, because this group collectively raised our expectations for rookies (just as Mike Trout and Bryce Harper made us more impatient with young players as a whole). Many have already soured on Corey Seager as a result of this, despite his struggles being more than acceptable for a 22-year-old rookie. With that in mind, I decided to check-in on the more prominent rookies of April - including those folk who made our top-100, and some who essentially came out of nowhere. Please note that all stats are for April only.
Corey Seager, SS, Dodgers
April - .250/.311/.396, 14 R, 2 HR, 12 RBI, 1 SB (1 CS), 89 wRC+ (106 PA)
Seager was the consensus top prospect in the game heading into 2016, and nothing that has happened so far should change your thoughts on the matter. He has struggled mightily at home (.182/.234/.295), which suppresses his overall line, but nothing jumps out as an issue otherwise. Seager's walk rate is a tick above-average, his strikeout rate is well above-average, and he's making consistently solid contact. His BABIP sat at .275 in April, and, given his current batted ball profile, that number could jump 20-plus points without much in the way of luck.
Nomar Mazara, OF, Rangers
April - .333/.392/.460, 10 R, 2 HR, 7 RBI, 0 SB (0 CS), 135 wRC+ (74 PA)
Mazara may have had the best pure hit tool in the minors, and that has been on display since he got the call to the Majors on April 10. The 21-year-old drives the ball from gap-to-gap, and has yet to tap into his natural raw power in a big way - but there should be more home runs to come, given that he'll play half of his games in Texas. Lefties have flummoxed him somewhat (.222/.267/.259), which was also the case in the minors. However, Mazara has proven to be capable of adjustments, and he seems locked-in to the starting gig at this point.
Trevor Story, SS, Rockies
April - .253/.314/.630, 19 R, 10 HR, 20 RBI, 1 SB (1 CS), 136 wRC+ (105 PA)
Story set the baseball newswire ablaze in the first week or so of the season, batting .333/.357/1.111 with 7 HR in his first six Major League games. His bat has cooled considerably since that point, as his 35.2% K% in April caught up with him, but he has remained productive nevertheless. Story has hit .250/.318/.700 with a pair of home runs in the last week, and his power is not merely a Coors Field illusion - 6 of his 10 home runs have come on the road. His batting average will likely remain in the .250 range, and few believe that his power is for real ... but he's still driving the ball with authority, regardless of the park.
Byung-ho Park, 1B, Twins
April - .227/.288/.561, 9 R, 6 HR, 8 RBI, 0 SB (0 CS), 132 wRC+ (73 PA)
Few players have been as hamstrung by their teams as Park, who has little to show for his six home runs; that is likely to continue to be an issue going forward, as well, barring a few big breakouts in Minnesota. The team has also been hesitant to give him a shot against LHP, as he has all of 6 PA against southpaws (he's hit .000/.167/.000 in those chances, for whatever it's worth). That being said, Park has been on a mini-tear as of late, batting .303/.333/.727 with 4 HR in his last ten games, and cutting his strikeout rate from 36.6% to 33.3% in the process. Things are trending up for Park, and he'll have every opportunity to show his worth.
Jeremy Hazelbaker, OF, Cardinals
April - .317/.357/.683, 11 R, 5 HR, 13 RBI, 2 SB (2 CS), 166 wRC+ (71 PA)
This is Exhibit A of the Cardinals Black Magic, as the 28-year-old Hazelbaker came as close to 'out of nowhere' as is possible in this day and age. He did not make John Sickels' top-20 Cardinals prospects list, nor did he earn a mention on BP's top-10. He's a career .264/.341/.434 hitter in the minors. And here he is, raking in the big leagues. Hazelbaker's underlying numbers do suggest that much of this is a fluke - his walk rate is below-average, his strikeout rate well below-average, and his .395 BABIP is bound for regression. I hesitate to doubt the Cardinals, particularly as they are using Hazelbaker largely as a platoon player - but it is difficult to foresee him being a starting quality player for much longer.
Aledmys Diaz, SS, Cardinals
April - .423/.453/.732, 18 R, 4 HR, 13 RBI, 1 SB (0 CS), 213 wRC+ (75 PA)
And this is Exhibit B. To be fair, though, Diaz was a prospect heading into this season, with many seeing his as a potentially above-average player with a strong hit tool and average or better pop. And this feels like a scorching hot streak for a player with solid overall potential. It just seems as though the Cardinals find these sorts of players growing on trees. Diaz's high contact approach (he's striking out in just 6.4% of his PA) should allow him to maintain a strong batting average, and he could end up with 12 to 15 HR, given the 4 bombs already in the bag. It should go without saying, though, that his slash line will come down significantly - and sooner rather than later.
Kenta Maeda, RHSP, Dodgers
April - 32.0 IP, 7.9 K/9, 1.7 BB/9, 46.5% GB%, 1.41 ERA, 2.79 FIP
If that contract didn't look like a bargain in January, it sure as heck does now. While Maeda's peripherals suggest that his ERA is something of a fluke (particularly the 92.2% LOB% and 6.5% HR/FB), there is nothing there that implies that he's anything other than a quality starting pitcher. His average strikeout rate doesn't stand out, but he limits walks and keeps the ball on the ground, and pitching in Dodger Stadium is sure to help.
Steven Matz, LHSP, Mets
April - 21.0 IP, 9.4 K/9, 3.0 BB/9, 55.2% GB%, 3.86 ERA, 2.73 FIP
The specter of injuries will always hang over Matz, but his performance as a professional baseball player has been nothing short of terrific. He lacks the sort of control that one would look for in a top of the rotation starter (though his walk rate is a tick above-average), but he picks up strikeouts and groundballs at an above-average rate, while limiting hard contact. He has had some bad luck with balls in play thus far (.393 BABIP), and the defense behind him has been shaky at times - but that ERA should improve at least a bit as the season wears on. His ERA is also skewed heavily in the early goings by a 1.2 IP, 7 ER performance in his first start of the season.
Aaron Blair, RHSP, Braves
April - 11.1 IP, 3.2 K/9, 4.0 BB/9, 34.4% GB%, 3.18 ERA, 3.69 FIP
I'm including Blair here as he appears to be up for good, despite an underwhelming performance thus far. He has done a fine job of limiting quality contact thus far (and inducing a ton of pop-ups in general), but he simply isn't getting swings and misses - his 6.1% swinging strike rate is well below the 10% league-average. As he acclimates to the big league, I expect his numbers to improve across the board; but on a bad team in front of a subpar defense, his fantasy value may not be terribly high.
Seung Oh, RHRP, Cardinals
April - 13.0 IP, 13.2 K/9, 4.2 BB/9, 39.1% GB%, 1.38 ERA, 1.53 FIP
Much has already been written about how unhittable Seung Oh has been thus far, and he seems to be in the mix for the team's set-up role at this point. His fantasy value is limited to bumping up rate stats and holds, as Trevor Rosenthal won't be losing the closer's role anytime soon, but he has been good enough to merit a spot in deeper leagues. And should Rosenthal go down with an injury, I wouldn't be shocked if Oh earned a shot over Jonathan Broxton and company.