Carlos Rosa was signed by the Royals in 2001, out of the Dominican Republic. He made his North American debut in 2002, posting a 6.19 ERA with a 11/12 K/BB in 32 innings in the Gulf Coast League, allowing 52 hits. Terrible numbers, obviously, but he was just 17 years old. At that point, he couldn't rate higher than a Grade C, a very young kid with a live arm and projectability, but with no otherwise distinguishing features.
He returned tor rookie ball in 2003, this time for the Arizona League Royals as Kansas City switched their spring training operation (and associated complex league team) to Arizona. He pitched better, with a 3.63 ERA and a 54/18 K/BB in 69 innings, with 79 hits allowed. He'd still rate as a Grade C prospect, making some progress but with much to prove at higher levels.
Rosa made eight starts for Burlington in the Midwest League in 2004, going 0-5, 4.67 with a 23/17 K/BB in 35 innings with 41 hits allowed. He blew out his elbow, having Tommy John surgery and missing all of 2005 on rehab.
He came back fully healthy in 2006, going 8-6, 2.53 with a 102/54 K/BB in 139 innings for Burlington, 121 hits allowed, followed by a 7.15 ERA but a 13/4 K/BB in 11 innings for High Desert in the Cal League. I saw him pitch for Burlington, and was impressed with his 90-93 MPH sinking fastball. His slider and changeup also showed promise, and his command was solid. I gave him a Grade C+ in the 2007 book, writing that I had "some intuitive optimism" about him, but that they would have to be careful not to rush him.
Rosa began 2007 with Wilmington in the Carolina League, going 2-1, 0.39 in four starts to earn a promotion to Double-A. He was mediocre for Wichita in the Texas League, going 6-6, 4.36 with a 70/43 K/BB in 97 innings, 101 hits allowed. When I saw him pitch for Wichita, he was throwing 89-91 MPH with his sinker, and his slider and changeup weren't as sharp as they were in 2006, although his curve looked good. Baseball America, on the other hand, reported Rosa hitting 95-97 MPH in their 2008 prospect handbook, which isn't what I saw. I gave him another Grade C+ in my 2008 Baseball Prospect Book, writing that Rosa would need a full year of Triple-A and that I saw him more as a fifth starter or reliever than a future ace.
Rosa went 4-2, 1.20 with a 42/7 K/BB in 45 innings for Double-A Northwest Arkansas this spring. He made two appearances with the Royals and looked quite good in 3.1 innings, fanning three with one run allowed. His Triple-A numbers were less impressive, though not bad at all for the Pacific Coast League: 4.09 ERA with a 44/12 K/BB in 51 innings, 51 hits allowed.
Rosa was getting a lot of attention this spring. If healthy I think he's a fine prospect, but health is an issue: he pitched just three innings since August 1st due to forearm soreness and is currently on the DL. If healthy, I think Rosa would be best-suited for long relief/spot starting work in the short run, with a shot at being a rotation starter in the long run. I like his ground ball tendency and command. I have him as a Grade B- prospect pending health status reports.