The mystery was quickly cleared up when the Royals sent Castro to the Rangers for second baseman Esteban German, who spent virtually the entire season with Oklahoma of the Pacific Coast League.
"He has a good repertoire and despite his size, he has a pretty big fastball in the low 90s," said Texas assistant general manager Thad Levine of the 5-foot-8 hurler. "He's going to compete for a spot in our bullpen with the other six-year free agents that we brought in. We think he can be more than a situational lefty. He's a big strikeout guy that causes a lot of awkward swings."
Castro's selection was first of 12 made in the Major League phase of the draft, 10 of which were pitchers. Overall, 65 players changed organizations Thursday morning, 47 of which moved in the Triple-A phase. Six additional players were selected in the Double-A phase, officially bringing an end to baseball's annual winter get-together.
The deal that sent the top pick to Texas wasn't the only one made, however. The Devil Rays grabbed Toronto right-hander Stephen Andrade, who spent the 2005 season at Double-A New Hampshire, to San Diego for cash considerations. Detroit, meanwhile, grabbed right-hander Chris Booker and then traded him to the Phillies for cash. Booker spent the season at Triple-A Louisville.
The most intriguing pick of the Major League phase was made by Florida, who selected Arizona prospect Dan Uggla. An 11th-round pick in 2001, Uggla had a breakout season with Tennessee in the Southern League, hitting .297 with 21 homers and 87 RBIs. He really made his mark in the Arizona Fall League, hitting .304 with seven homers and 22 RBIs in 102 at-bats for the Peoria Javelinas.
Having already dealt Luis Castillo to the Twins, the Marlins are looking at Uggla as their possible starting second baseman.
"He enhanced his value during the Fall League but we scouted him during the year," Florida vice president for scouting and development Jim Fleming said. "You've seen what's gone on [with the Marlins] the last few days, so I'd say yes, he has a chance."
The Cardinals also made a potential impact selection, choosing right-hander Juan Mateo from the rival Cubs. Mateo, who'll turn 23 next week, was 10-5 with a 3.21 ERA at Single-A Daytona, picking up 123 strikeouts in 109 1/3 innings. He figures to vie for a spot in the St. Louis bullpen.
"He's got a good arm," said John Vuch, the Cards' assistant director of player development. "His fastball (90-93) is his best pitch. He has a good changeup and a slider that's inconsistent. That's the one thing we'd like to see, consistency on his slider. He shows it at times. He's shown good command, has a good arm but also has an idea how to pitch."
The Devil Rays, Royals and Cubs were among the more active teams on Thursday. Including Andrade, Tampa Bay selected five players while losing three. Kansas City saw five of its prospects selected while grabbing two from other organizations, including Castro. Chicago, meanwhile, also lost five players, including three pitchers from Double-A West Tennessee. The Cubs did grab three players in the Triple-A phase, though, to offset the losses.
Milwaukee lost four players -- all from their Double-A Huntsville roster -- and added one. Pittsburgh selected five players, including right-hander Victor Santos from Kansas City in the Major League round. The Pirates lost two players in the Triple-A phase, so they came out ahead. The Red Sox grabbed four players, including right-hander James Vermilyea in the Major League round, while losing only two.
"You can't protect everybody," said Oneri Fleita, Chicago's player development director. "That's what happens when you get better -- you can't protect everybody."
The Cubs, however, also parted ways with Minor League pitchers Sergio Mitre, Ricky Nolasco and Renyel Pinto earlier this week in the deal that brought Juan Pierre from Florida.
"You'll certainly miss them," Fleita said. "You don't want to lose any of your players. A lot of times we get very close to our players, especially in the development side. We had those guys from day one, when they were young kids out of high school."
Kevin Czerwinski is a reporter for MLB.com. Matthew Leach, Carrie Muskat and Robert Falkoff contributed to this report. This story was not subject to the approval of Major League Baseball or its clubs.