Castro is batting .356 with 13 extra-base hits and 20 RBIs through 24 games, and his hitting isn't necessarily the most impressive part of his game.
The native of the Dominican Republic is making spectacular plays along with all the routine ones, having committed just three errors.
"He's got plus range, a plus-plus arm and he's so smooth he even makes bad ups look good," Smokies manager Bill Dancy said about Castro's defense.
He not only takes away hits, he gets a lot of them himself. Despite his glove work, you can't overlook what Castro does at the plate.
"What impresses me the most is the way he's hit in the clutch," Dancy said. "He's really a tough out."
Castro showed that by hitting .376 in the Arizona Fall League and was even more impressive in batting .423 in Cactus League games this spring with the Cubs, although he didn't turn 20 until March 24.
"The good ones come quick," Cubs manager Lou Piniella told reporters this spring. "The player will tell you if he's ready or not."
According to Cubs general manager Jim Hendry, there are no immediate plans to promote Castro to Chicago. But the time can't be too far off.
Castro, meanwhile, insists that he is remaining patient.
"I will be excited when the time comes, but I'll wait for them to make the call," Castro said. "I'm just playing every day and trying to get better."
Having played just one season above rookie ball coming into this season, Castro had some rough edges to refine. But he seems to have done that, cutting down on bad throws and no longer chasing pitches outside the strike zone.
"I learned something every day," Castro said of spending Spring Training with the Cubs.
For Castro, it is all about learning to stay within himself and sticking with the fundamentals. "Last year I made a lot of errors on throws," he said. "This year I'm trying to be more consistent."
The same goes for plate discipline, and Castro has nine walks and 11 strikeouts in the Smokies' first 24 games. "I'm waiting to see more good pitches," Castro said. "That will help me when I get to the Majors."
Having grown to nearly 6-foot-3 and weighing more than 190 pounds, Castro is showing more and more power. Six of Castro's 15 hits with the Cubs this spring went for extra bases, and he has eight doubles, four triples and a homer for Tennessee.
Castro does need to work on better utilizing his speed on the bases, having been caught five times in nine stolen-base attempts.
When the Cubs deem Castro ready for the Majors, Ryan Theriot will likely move to second base.
"I don't have any doubts you'll see him in Chicago this season," Hendry told ESPN Radio last week when asked about Castro. "But to put an exact date on it would be foolish."
Homer tear: Jacksonville's Mike Stanton has nine homers in his last nine games, raising his season total to 13 -- the most in the Minors. The outfielder also leads the Southern League with 29 RBIs and has a .515 average in his past 10 games. Stanton, 20, sports a .504 on-base average thanks to a league-best 25 walks.
Red-hot hitter: West Tenn OF Carlos Peguero sits second in the league batting race with a .379 average. He followed a four-hit game that included three homers with a pair of two-hit games. Peguero, 23, has 10 homers and 20 RBIs.
Staying perfect: Mississippi Braves reliever Stephen Marek has not allowed a run in his first 10 appearances, recording 17 strikeouts with just one walk in 12 innings. The 26-year-old right-hander was acquired from the Angels as part of the trade for Mark Teixeira in 2008.
Suns heat up: Jacksonville took over first place in the South Division thanks to a 10-game winning streak. The streak was broken Friday by Mississippi, which won, 5-4, at the Baseball Grounds. The Suns' streak included sweeps of Birmingham and Carolina.