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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Houston: Freudis Nova, SS (No. 5 on Astros Top 30)
Nova looked destined to sign with the Marlins for $2.5 million out of the Dominican Republic, but that deal disappeared when he tested positive for performance-enhancing drugs in February 2016. After he passed several subsequent drug tests, the Astros landed him for $1.2 million five months later. The best prospect from their franchise-record $17.5 million spending on bonuses and penalty taxes for international players in 2016-17, he has drawn comparisons to Hanley Ramirez and Edgar Renteria.
Houston loves Nova's tools as well as his performance in various analytic measures of strength, speed and condition. He has bat speed and loft in his right-handed stroke, shows promising plate discipline, has the quickness to steal bases and the tools to stay at shortstop. He batted .247/.342/.355 as a 17-year-old in the Rookie-level Dominican Summer League in 2017 and could jump to low Class A for his U.S. debut this season.
"He's so explosive," Astros farm director Pete Putila said. "He's a legitimate shortstop with power and contact and speed. He drew walks in the DSL and when he chases, he still barrels the ball. He has a good mindset. He's not distracted, he keeps working."

Los Angeles: Jerryell Rivera, LHP (No. 22 on Angels Top 30)
Rivera was an under-the-radar high school lefty in Puerto Rico who was seen by many as a soft-tossing southpaw. The Angels thought there was more in the tank and took him in the 11th round, giving him $450,000 to sign. He pitched well, albeit sparingly, during his pro debut in the rookie-level Arizona League, and he's already added some ticks on his fastball since signing.
"He's incredibly athletic," Angels director of Minor League operations Mike LaCassa said. "He has an advanced feel from what we may have thought prior to him becoming an Angel, both with his fastball command and his changeup, which is his best secondary pitch. He continues to get better at a pretty impressive pace."
Oakland:Sean Murphy, C (No. 8 on A's Top 30)
Undrafted out of high school and a preferred walk-on at Wright State, Murphy emerged as a Louisville Slugger Freshman All-American and earned All-League honors in 2015-16. After becoming the second-highest pick in Raiders history when the A's drafted him in the third round, Murphy earned California League All-Star honors (after bypassing the Class A level) before a midseason promotion up to Double-A. The 23-year-old backstop elevated his stock even more in the Arizona Fall League with a standout performance on both sides of the ball against advanced competition.
One of the better catch-and-throw backstops in the Minors, Murphy stymies the running game with plus-plus arm strength and above-average pop times, so much so that only 46 baserunners attempted to steal against him over 91 games in 2017. At the plate, the right-handed hitter exhibits a strong approach with natural hitting ability and raw power to his pull side.
"He didn't have a lot of technique but he had very good hands," A's director of player development Keith Liepmann said. "He'll learn a lot in big league camp, pitch calling and sequences. He's a sponge. He has an eight arm -- he can really throw. He's got a really good demeanor and has a chance to be a gap-to-gap guy, maybe 15 homers a year. He's just got to learn to use the opposite field a little more."

Seattle: Wyatt Mills, RHP (No. 10 on Mariners Top 30)
Mills opted to return for his senior season at Gonzaga, in the process passing on a 17th-round selection by the Rays, and turned in a dominant campaign, as he posted a 1.79 ERA and 12 saves to finish with the second-most saves in program history (21). The Mariners made Mills their third-round pick in June, and he proved to be far more than just a money-saving senior discount during a stellar pro debut in which he reached full-season ball.
A side-armed right-hander with two above-average pitches, Mills pairs a low-90s fastball that touches 95 mph with a tight slider. The combination makes him highly effective against same-sided hitters, and he's already impressed Mariners club officials with his ability to throw strikes from his unique slot.
"Mills is a kid we talked about in our top five rounds," Mariners director of amateur scouting Scott Hunter said. "He reminds me of Joe Smith and Steve Cishek. A guy with a unique arm slot, and the ability to throw as many strikes as he does … From the angle he's doing it from, he could be a quick mover, if he keeps doing the same things."

Texas: Hans Crouse, RHP (No. 4 on Rangers Top 30)
Crouse had one of the best high school arms in the 2017 Draft, as well as a track record of success against top competition, but the effort in his delivery and his animated demeanor on the mound left some clubs unsure what to make of him. The Rangers loved his stuff and his makeup, so they gladly paid him an over-slot $1.45 million bonus when he dropped to them in the second round. He was spectacular in his pro debut, logging a 41 percent strikeout rate and a .109 opponent average in 20 Rookie-level Arizona League innings.
Crouse can destroy hitters with a mid-90s fastball that features riding life, as well as with an overpowering slider than he can manipulate into a power curveball when he wants. He also shows some promising fade on a changeup that should be a solid third offering once he develops enough separation in velocity from his heater. Though he has a lot going on with his mechanics, he keeps them in sync enough to find the strike zone on a consistent basis.
"He's so unique," Rangers assistant GM Josh Boyd said. "He has a pair of huge plus pitches and throws strikes. He regularly hits 99 mph and he has a wipeout slider. It's a unique delivery, but he repeats it and he's on time."