In his first full season last year, Castro led the National League in hits with 207, but he also committed the most errors in the Majors at shortstop with 29. Asked what he needs to improve upon, Castro doesn't hesitate.
"My defense," he said. "I've been working hard on my defense and running bases and trying to steal more bases and focus more."
That's what he told Sveum as well when the manager had his one-on-one chat with Castro before workouts began. The Cubs tried to give the shortstop a head start this winter by sending Mariano Duncan, a 12-year Major League veteran, to the Cubs academy in the Dominican Republic to work with Castro. It's obvious during practice that Castro has a great arm. He just has to set up better defensively and pick up the target better.
"There are certain reasons why he makes throwing errors," Sveum said Sunday. "One is because he picks up his target too late. ... He has a tendency to get a ground ball and look over his shoulder and then it causes his shoulder to turn and then it has to open up and that's why you see the ball go down or they fly high.
"If he keeps everything straight and focuses on the first baseman, it's a much easier play. A lot of young guys tend to do something like that or they pick up the runner when they're running down the base, and it just causes problems."
Sveum has given Castro pointers every day, and every day it's another lesson.
"One fundamental that a lot of young players have is just not gaining ground when the ball is hit," Sveum said. "I call it 'squatting' -- you see a ball hit so you stand in the same spot and let the ball get to you. It's not charging the ball, it's not the dreaded term, 'Don't let the ball play you,' because only God knows when it's going to take a bad hop.
"It's just a matter of understanding when you gain ground on ground balls, you're going to throw the ball five yards less, your feet are going to be moving," Sveum said. "It's a work in progress."
Which is why coach Pat Listach will stay close to Castro during infield drills. It's up to Listach to remind the shortstop about his positioning, about his glovework, his head, his footwork. It's all part of his education.
Castro was promoted from Double-A to the big leagues in May 2010 after three seasons in the Minor Leagues. He showed he could hit, belting a three-run homer in his debut at-bat, and finishing his first game with six RBIs. He's put together back-to-back .300 seasons and has the potential to increase his home run total after hitting 10 last year.
He just has a lot to learn to become a well-rounded player. What's encouraging is that Castro isn't fighting the instruction; he's welcoming it.
"The few things I've asked him to do or Pat's asked him to do, he's pretty much done it," Sveum said Sunday. "Today was great. Covering ground when a ball is hit, he wasn't staying back by the grass. Once I talked to him about moving his head, he stopped doing that and started making really good throws. I think when you have success, too, that always helps. You understand, 'Oh, that's all I've got to do to change?' A lot of times it's not major stuff. Sometimes it's the simpler stuff."
What the Cubs want is another All-Star season at the plate and to see improvement on the field.
"I had a great winter, preparation, to get ready on the field," Castro said. "I'm ready to play baseball."
Sveum hasn't set his lineup yet, hinting only that David DeJesus will lead off and Bryan LaHair will bat fourth. Castro primarily led off last season, hitting .327, but he also hit .335 in the No. 2 hole and .225 in 42 games batting third. Castro may be most comfortable batting first or second, but Sveum said he expects he'll need the shortstop elsewhere in the lineup. Would Castro like to be the No. 3 hitter?
"Yeah, I want that," Castro said. "[Sveum] told me something about that. He said, 'The three-hole,' and I said, I don't care, hitting first, second or third, I'll try to do my job."
He's shown the ability to learn. When Castro first came up, he relied on an interpreter for TV interviews. He handled his first media session at Fitch Park this season by himself. He was complemented on his English, and asked if he'd been told any "bad words."
"In the beginning, that's what you learn first, but now, I take it out," Castro said, smiling. "No more."
He's growing up.
"Castro is a good kid, he's got a great future ahead of him," Duncan said, "but he has to understand what we're trying to teach him and make him do it. We believe he has a chance to be an All-Star shortstop all the time. He plays every day, he enjoys the game, he loves the game.
"I know he has a great attitude. I'm going to try to do anything I can to help that kid. We have a future superstar at that position. I believe he can do that."
What may help Castro most is that his new manager understands the process.
"I can relate to Castro when I was young," Sveum said. "I made a lot of errors and some of the things I'm telling him are some of the same things I had. Things like that happen to a lot of people.
"My best friend, Robin Yount, made 80 errors his first two years in the big leagues," Sveum said of the Hall of Famer. "He turned out to be a pretty good defensive player. The will has to be there to do it."
Asked about his new manager, Castro smiled.
"I like him," Castro said.