Last season, the shortstop found out what it's like to have a bad year. He struggled to bat .245 and struck out a career-high 129 times, a significant change after hitting .300 each of the three previous years. A two-time All-Star, he looked like anything but in 2013.
"This is a tremendously gifted individual who has obviously not had or played the way he's capable of playing," Cubs manager Rick Renteria said. "We have to address certain things. We have to figure out what's making him tick or not tick the way we want him to tick."
Castro took a big step this offseason by devoting more time to workouts. For three weeks in November, he trained six days a week at his Dominican Republic home with Cubs strength coach Tim Buss. Castro spent another four weeks at the IMG Academy in Brandenton, Fla., doing agility drills and conditioning as well as working on his baseball skills.
"It was really hard," Castro said about 2013. "I never had a bad season like that one. It's tough for me, especially when I went home, and I think about myself, and think 'Wow.' I tried to be strong, clear my mind and think about this year."
Renteria has been thinking about Castro, too. During his chat with the media on Tuesday, the new Cubs manager got his pronouns mixed up after a question about expectations for Anthony Rizzo and started talking about Castro instead.
There has been a lot of attention on Castro's mental lapses, Renteria said. While working out recently, the manager saw highlights of some players' low moments when they forgot how many outs there were in a game, such as outfielder Larry Walker, who once handed a ball to a fan, not realizing it was only the second out. Castro's brain cramp moment, when he caught a popup in shallow left and a runner scored from third, got a lot of attention.
"It happens to the best of them," Renteria said. "You talk to all those guys [who made mistakes in the past] and they're all laughing about it now. Unfortunately for this young man, everybody decided he was the one to pick on, he was the one to make a big emphasis about what just occurred.
"I get it," Renteria said. "It's a situation where it's a club not performing as well as everybody would want. You wouldn't want those things to occur. We don't expect them to continue to occur, but I think this is a new year, hopefully a new environment, where high expectations are being laid for everyone. It's incumbent on all of us as coaches to understand how these guys work and do things and help them stay on their toes as the game is progressing."
Castro says he's willing to do early work every day with the infield coaches if they want. How can he eliminate the mental mistakes?
"Just work on it," he said. "Just try to concentrate. If the game is three hours, four hours, try to concentrate for four hours, no matter what happens out of the game."
The other Cubs players know Castro is key to the team's success.
"I know he has a chip on his shoulder," second baseman Darwin Barney said. "I know he knows he's a better player than his numbers showed last year. I know he's ready to move on in his career and put last year behind him. He worked really hard this offseason and I've heard only good things from [Buss]. He was really working with a passion that we all saw early in his career and I think he'll be fine this year."
"Whenever we do talk, we usually talk about taking care of each other, and not necessarily proving people wrong but going out and playing our game," Barney said. "We both know we're better players than we were last year. We think that defensively we'll be even better this year. I think we'll work well up the middle. I know he's excited about the fresh start."
It's a fresh start with a new manager.
"Clean," Castro said of his approach to 2014. "I try to put in my mind nothing about last year. I'm just going to be myself, keep my mind clean and be ready to play baseball."
The Cubs do have highly touted shortstop Javier Baez waiting in the wings. Baez, the Cubs' Minor League Player of the Year in 2013 who belted 30-plus home runs and drove in more than 100 runs, will open at Triple-A Iowa this season. Castro isn't worried, calling Baez a good friend.
"I said, 'Play hard. You play hard, you'll be in the big leagues soon,'" Castro said of his advice to Baez.
Ryan Theriot told Castro the same thing in Spring Training 2010. Then, Castro took Theriot's job.
"Castro is our shortstop," general manager Jed Hoyer said of the infielder, whom the Cubs rewarded with a seven-year, $60 million contract in August 2012. "We have all the confidence in the world that he'll remain our shortstop."
Baez may play some second or third this spring, but he'll stay at shortstop in the Minor Leagues.
"You never want to remove a shortstop from shortstop," Renteria said. "So if we have the luxury of having Starlin at the Major League level and [Baez] at Triple-A shortstop, why wouldn't we do that? [Baez] is a guy who has impressed everybody and he has some skill and we want him to continue to improve and mature and be the player we hope he will become in the end."
Castro could be the Cubs' leadoff man this season, even though his aggressive approach at the plate doesn't seem to make him an ideal candidate. That's fine with the shortstop. He likes hitting at the top of the order, and says he'll do whatever Renteria wants. It's a long way from last season when Dale Sveum briefly dropped Castro to eighth in the order.
Sveum, dismissed after two seasons as the Cubs manager, pulled Castro out of a game after a mental mistake. Was he too hard on the shortstop?
"Nah, just normal," Castro said.
Renteria has the edge already because he is bilingual.
"There are a lot of Latin players here who don't understand English very good," Castro said. "It's really important that he speaks Spanish because sometimes when you're [ticked] off or whatever, he can tell you in Spanish and you can understand better than if he says it in English."
Hopefully, there won't be many conversations like that.
Castro will turn 23 on March 24. His son, also named Starlin, will celebrate his first birthday four days later. It's quite a change for the young, gangly shortstop, who now finds himself one of the leaders on the team. Gone is his mentor, Alfonso Soriano. The two talked during the offseason.
"He told me, 'You have pressure this year,'" Castro said. "'You have to come into Spring Training, look good, be ready because everybody is looking at you after you had a tough year, so try to let your play take over now.'"
But Castro doesn't want to be labeled a leader.
"My responsibility is to play hard," he said. "The other guys behind me look at me, and say, 'I want to be this guy because that guy works hard and plays hard.' I don't want to be a leader because there are 25 men on the team."
Last spring, Barney had gloves stitched with Cubs blue and red stripes for both he and Castro. Middle infielders have to stick together.
"He's definitely going to come out with some good desire this year, which will be fun," Barney said.
Castro is pumped.
"I had a lot of motivation," he said. "People here are on top told me, 'Don't listen to too many things, try to be me.' That motivates me. I try to be me, do what I do, do always what I do and try to concentrate on my work."