Each week in this report, I’ll be monitoring the performances of MLB rookies. I will emphasize those rookies who put up especially positive performances, while also taking care to mention rookies who are underperforming expectations. In both cases, I will dig into the underlying stats and attempt the difficult task of projecting forward.

Rookies are typically more unpredictable than their more experienced colleagues, and can, therefore, be a source of great profit in fantasy baseball, or great frustration. Stay tuned to this space every week to find out which newbies should be in the mix for your squad. Check out last week’s Rookie Report to keep up to date on all the hottest youngsters.

Stats are generally current prior to Tuesday’s games, and, as noted in week 3, any quoted Statcast numbers are directly from Baseball Savant.

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Quick Updates: Cody Bellinger and Trey Mancini

After cooling off in May, Cody Bellinger has come out smoking in June with 13 homers, rising to the top of the NL charts. His .404 wOBA is not quite supported by his .376 xwOBA, but his 98.3 mph average exit velocity on liners an fly balls ranks in the top-10 of players with more than 30 batted-balls. His contact rate leaves something to be desired, which could lead to additional slumps over the course of the year, but he has firmly (and quickly) established himself as a top-tier player, even kicking in five steals in five attempts.

Likewise, Mancini has been on the upswing of late with seven homers of his own to go along with a .365 average. He has also been playing nearly every day due to Chris Davis’ oblique injury. He too sports an xwOBA (.365) slightly below his actual mark (.397), neither much off Bellinger’s pace. While he may not hit above .300 the rest of the way, Mancini is becoming an increasingly solid, sneaky source of batting average. With continued playing time, something he has earned, Mancini seems poised to approach 30 homers while being a positive contributor in offensive ratios.

Paul DeJong (2B/3B – STL)

Paul DeJong was not a highly touted prospect, falling at 227 in the consensus prospect rankings and 350 in Bobby Sylvester’s rankings. While his bat speed and hard contact ability make his bat intriguing, he was expected to have strikeout issues and unlikely to stick at the premium shortstop position. Still, DeJong has slashed .286/.294/.524 with five homers in his 23-game MLB debut, building upon his .909 OPS in Triple-A to start the season. Playing mostly second base, DeJong is also eligible at third and has also appeared in four games at short, opening the possibility of triple eligibility at some point this season. All is not rosy with DeJong, however. His microscopic 1.2% walk rate and 31.8% strikeout rates are poor, and his .256 expected batting average (xBA) and .302 expected wOBA (xwOBA) are both well below his .286 and .341 current marks. Both are in line with his rest-of-season projections, which do not add up to a special fantasy asset. Especially if he does not gain shortstop eligibility, DeJong is not worth rostering in most mixed formats. Further, if Kolten Wong is back after the All-Star break, DeJong may find himself back in the minors.

Matt Olson (OF – OAK)

Walks, strikeouts, and homers. Stop me if you’ve heard this young player refrain before. Except, in the case of Matt Olson, the archetype doesn’t quite hold. With the exception of his debut season in pro ball, Olson has always posted walk rates well above 10%. After a blistering 2014 season at High-A where he hit 37 homers, Olson has tallied exactly 17 at each minor league level since, most notably hitting 17 in the early going this season at Triple-A. And while he usually sits over 20% K%, Olson does not have any seasons above the alarming 30% rate. Olson did not enter the season as a highly-ranked prospect and has posted an interesting .174/.387/.478 line so far, with seven walks and nine strikeouts in 10 games. The two homer power output has been nice, but a sub-.200 batting average with near-30% strikeout rate illustrates the downside of Olson. With a 97.5 mph average exit velocity on liners and fly balls and a 14.3% Barrels per batted-ball rate, Olson has definitely hit the ball hard, but his average is likely to be enough of a liability that owners should monitor, but not invest just yet.

Franklin Barreto (SS – OAK)

In contrast to teammate Olson, Franklin Barreto has long been a top prospect, coming to the Athletics as part of the Josh Donaldson trade. Earning high marks from scouting types, and sitting at 25 and 18 in the consensus and Sylvester prospect rankings, Barreto is among the top prospects to be called up so far in the 2017 season. Scouting the stat line, however, may temper the short-term fantasy enthusiasm. Barreto posted above average batting lines at nearly every minor league stop, while being young relative to his levels. His .753 OPS at Double-A last year was somewhat uninspiring, especially including the substandard 66.7% success rate he achieved in compiling 30 steals. Oakland is 28th out of 30 teams in steals this year with the 26th-best success rate, indicating a relative unwillingness to run wild. With 32 HR in 1,198 plate appearances since the start of 2015, Barreto is certainly not a pure slugger. Barreto does not walk much and he will need to keep an eye on his strikeout rate that began to balloon at Triple-A, which likely means he will not be an above average contributor in AVG or OBP right away. One homer and an 84.2% contact rate in his first 10 MLB plate appearances are nice to see, but the safe money is on Barreto taking some time to mature into a productive hitter. However, the reality of the shortstop position in fantasy baseball is such that anyone with upside can be worth a flier. Barreto certainly has upside, and desperate owners are not guaranteed to see a better SS call-up this season.



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Andrew Dominijanni is a correspondent at FantasyPros. For more from Andrew, check out his archive and follow him @ADominijanni.