Rosa was an international signing, at the age of 17. Here's his performance in the Orioles' minor league system so far, listing only leagues with at least 150 PAs in a season, and the predicted chances of making the majors, MLB success, and stardom given that year's results.
Age League PA Triple/ OPS K% Prospect? MLB/Succ/Star 17 DOSL 225 .275/.290/.375 .665 19.6% ----- ------ 18 GCL 192 .330/.339/.470 .809 13.5% YES 43.0%/16.4%/9.8% 19 NYPL 239 .218/.263/.391 .654 30.1% NO (Ks) ------ 20 SAL 478 .251/.271/.362 .632 23.8% NO (OPS) ------ 21 SAL 257 .262/.278/.369 .647 22.2% NO (OPS, Ks) ------ 21 CARL 187 .212/.225/.296 .521 25.1% NO (OPS) ------ 22 CARL 389 .245/.272/.358 .630 22.4% YES 16.6%/3.9%/0.3% 23 EL 477 .276/.291/.374 .665 16.1% YES 30.8%/2.3%/0.0% 24 EL 80 .373/.392/.547 .939 16.3% YES* 68.4%/17.7%/7.7%* *Sample size too small! Needs 150 PAs for a single league-year to be valid.
Rosa was OK in the Dominican League; I can't quantify performances at that level. He displayed moderate pop, acceptable for a middle infielder, good contact, very low walk rate and a lot of Ks. In the GCL, he had similar results with a bit more power and much better BABIP luck; as a result, he had a strong .809 OPS which gave him a reasonable chance to be successful (very few GCL 18 year olds have chances over 20-25%), and even a decent chance at future stardom. However, he was never able to get the same level of contact, and with a low walk rate, only moderate (.100-.160 ISO) power and lots of Ks, wouldn't have qualified as a prospect per me at any point over the next three years. He was usually close to, but below, the cutoff.
In 2012, he had all the usual issues, but a slightly improved contact rate and a slightly reduced K rate brought him just over the age-22 Carolina League prospect cutoff (.620 OPS). He profiled as pretty marginal, with just a slight chance at ever being productive. The story repeated itself next season: just enough production to qualify as a prospect with a small chance of ultimate success. Notably, his strikeout rate fell quite a bit in the Eastern League, and he had his highest batting average since his great year in the GCL.
This year, nothing has really changed as a hitter. He still doesn't walk, and the power is up just a bit (.174 ISO), which is a little high but not out of Rosa's ordinary. His BABIP is way up, and the usual response to this profile is: small sample size that will correct itself soon enough. The one ray of sunshine is that his K rate has stayed at the same (relatively) low level as last season. Rosa will be a real prospect if and only if he has managed to turn some of his Ks into balls in play, falling for a few extra hits thanks to speed. With this reduced K rate, a line of .300/.320/.430 might not be an unreasonable target.
I've provided a projection based on Rosa's current OPS this season, but these will only hold valid if he maintains his current level of production all year. Any projection of success chances for a player with fewer than 150 PAs has no validity at all - those numbers are just for illustration. If Rosa can keep it up, he'll be a real prospect, though not a great one, since he's a bit old. You should probably push his chances up a few percent thanks to his position; the projection system does not take his middle-infield defense into account.
Overall, I think Rosa remains a marginal prospect, but one worth watching. If his K rate stays down and his BABIP stays up, he has a solid chance to be a MLB success, generating a few WAR over a career as a utilityman or spot starter, with the ability to play SS in a pinch or 2B/3B well. I think the most likely interpretation right now is that we are seeing a SSS-driven, BABIP surge, and Rosa will fall back to his usual strikeout-plagued self. Still, an unusual spike of good performance is notable, and we'll see if it keeps up.
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