Some prospects are highly touted heading into a season and then live up to advanced billing. Others are a bit more under the radar, either because they are coming off of injuries, haven't performed up to expectations or perhaps are just getting started on their pro careers. MLB Pipeline selected one of these type of prospects from each organization as a 2018 breakout candidate. We might not be talking much about the prospects below now, but they could jump on the scene in a big way this season.
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Baltimore: Matthias Dietz, RHP
Scouts viewed Dietz as the top junior college prospect in the 2016 Draft after his breakout sophomore season at John A. Logan (Ill.) CC in which he went 12-1 with a 1.22 ERA and 117 strikeouts (in 103 innings), ranking among the JUCO leaders in all three categories. The Orioles made him their second round pick that June, only to watch Dietz scuffle in professional ranks as he struggled to repeat his delivery. Spending his first full season with Class A Delmarva, the 22-year-old right-hander posted a 3-10 record with a 4.93 ERA, a 1.50 WHIP and a 92-to-50 strikeout-to-walk ration across 129 2/3 innings (26 starts).
Given his age, experience and large, physical frame, Dietz was expected to be the type of project he's been early in his career. He did make improvements during the second half in the South Atlantic League as well as in the fall instructional league, and Dietz's strong spring has the Orioles thinking the big righty might be ready to take another developmental stride back at Delmarva in 2018.
"By numbers, he had a sub-optimal year in Delmarva last year," Orioles farm director Brian Graham said. "But this spring, he's been 95-98 mph, commanding the baseball, pitching down in the strike zone, showing the ability to throw a breaking ball in the strike zone. He's a guy you look at, if you just read his stats, he doesn't look very impressive, but if you watch him on the mound this spring, your eyes open."

Boston: Pedro Castellanos, 1B (No. 18 on Red Sox's Top 30)
The Red Sox exceeded their international bonus pool in 2014-15, which subjected them to spending limitations in the next two signing periods, yet they landed one of the most promising hitters in their system with a $5,000 bonus in 2015. A Venezuelan, Castellanos hit .323 with a Rookie-level Dominican Summer League-best 23 doubles in his 2016 pro debut. Last year, he nearly won the Rookie-level Gulf Coast League batting title, finishing second by .001 at .339, and helped Greenville capture the South Atlantic League championship after a late promotion to low Class A.
Ticketed to return to Greenville in 2018, Castellanos has a mature approach for a 20-year-old, making consistent line-drive contact from gap to gap. He hits the ball hard and rarely strikes out, and he should begin to tap into the raw power he displays during batting practice once he adds some strength to his 6-foot-4 frame. He has seen most of his professional action at first base, though he moves well enough and has enough arm strength that he has gotten action on both outfield corners as well.
"He's big and physical," Red Sox farm director Ben Crockett said. "He's not a traditional lofting power type of guy but a guy who really has a feel to hit, uses the whole field, drives the gaps, can hit the ball over the fence. It's an advanced approach for such a young kid."
New York: Luis Medina, RHP (No. 7 on Yankees' Top 30)
The Yankees are making a habit of churning out one power right-hander after another, and the next one who's going to start making some noise if Medina. Signed for $280,000 out of the Dominican Republic in July 2015, he has recorded a 4.98 ERA with a 43/28 K/BB ratio in 43 1/3 innings during two years or Rookie ball. But those lackluster statistics belie his remarkable arsenal.
Medina isn't extremely physical at 6-foot-1 and 175 pounds, but his lightning-fast arm generates 95-102 mph fastballs with natural cutting action. He has a high spin rate on his power curveball and splitter action on a low-90s changeup, both of which can make hitters look bad. He needs more consistency with his mechanics and control to truly dominate, though time is very much on his side because he won't turn 19 until May.
"He has our highest ceiling," Yankees pitching coordinator Danny Borrell said. "He might have our best fastball, curveball and changeup. He'd go 1-1 in the 2018 Draft if he were part of it. It's just experience with him, getting consistent with his delivery. He averages 97 mph with his fastball but it's a controlled delivery, so he should have solid-average command. You'd be hard-pressed to find anyone with a better arm in the Minor Leagues."

Tampa Bay: Genesis Cabrera, LHP (No. 22 on Rays' Top 30)
Signed out of the Dominican Republic in November 2013, Cabrera made the jump to full-season ball three years later and earned mid-season All-Star honors in the Class A Midwest League at age 19. The left-hander built on that progress with his success at a pair of levels in 2017, beginning the season in the Class A Advanced Florida State League and then advancing to Double-A at age 20 late in June. He pitched well at both stops, finishing the year with a 3.22 ERA, a .240 opponents' average and 111 strikeouts in 134 1/3 innings.
Cabrera may be wiry, listed at 6-foot-1, 170 pounds, but his arm is lightning-quick that helps him generate a 92-95 mph fastball as a starter that can reach 97 in shorter bursts. He also has feel for both a slider and a changeup and is adept at changing hitters' eye levels from his over-the-top release point, with an ability to repeat to his delivery that only will improve as Cabrera adds strength to his frame.
"He was 95-97 mph from the left side the other day," Rays director of Minor League operations Mitch Lukevics said. "He'll start in Double-A."
Toronto: Kevin Vicuna, SS (No. 23 on Blue Jays' Top 30)
Vicuna has blossomed into one of the finest defenders in Toronto's system since signing for $350,000 out of Venezuela at the outset of the 2014-15 international period. That defensive ability enabled him to handle shortstop duties at age 19 for Class A Advanced Dunedin early in the season, from April 23 to June 1, after an injury created an opportunity for him. Vicuna otherwise spent his season showcasing his defense and hitting ability in the Class A Short Season Northwest League before advancing to Class A Lansing in mid-August.
The lithe-framed Vincuna has ultra-athletic actions, with quick, twitchy hands that help him absorb anything hit his way and execute a fast release that in turn helps his average arm strength to play up. And while he generates well-below-average power with his right-handed swing, Vicuna does have good bat-to-ball skills and a sound approach.
"We had an opportunity in High-A last year and identified him as someone with the defensive ability and acumen we thought he'd be able to handle that challenge up there -- he held his own up there," Blue Jays farm director Gil Kim said. "He's probably one of the top defenders we have at shortstop - that's sometimes a challenging skillset to develop in an organization. He's committed himself to his physical development and improving his overall body strength, and we're excited about what he might do this year."