NEW YORK -- The Chicago Cubs clubhouse hardly houses a recognizable name these days. Unproven rookies and past-their-prime veterans intermingle, each trying to earn their place in this rebuilding franchise, and if not there, then somewhere else with another team. The Cubs are a team in transition, and it's best for fans and players not to get too attached.

The Cubs have one of the most highly regarded farm systems in baseball, so soon some of these rookies and veterans will be replaced by even younger, less recognizable players. And judging by their early-season performance, the rebuilding under Theo Epstein will continue for at least a couple years yet. The days of Sammy Sosa, Mark Prior and Kerry Wood, and Moises Alou having a ball taken from him in foul territory during a critical playoff game are long past.

In the corner of the visiting clubhouse at Yankee Stadium one day this week, shortstop Starlin Castro slumped in his chair in the early morning. He grasped at the top of his head to wake himself up. His eyes were groggy with sleep. He shook his head, desperate to gain focus, but in those moments, it did not come. But there was still time. Game time wouldn't come for several more hours.

Focus seems to be a never-ending theme with Castro. A long day was expected, which presented a challenge in that regard.

A game against the Yankees had been rained out the previous day, so the two teams were scheduled to play a day-night doubleheader, which is quite possibly the worst possible scenario for a player like Castro. A day-night doubleheader means a day at the ballpark that can last almost 15 hours. Even the most conscious players would have a difficult time focusing for so long.

Castro is one of the first to arrive at the ballpark, which says something good about a player who is as big a name as it gets with the Cubs these days. If there was anyone who would want to parade himself and act like a big leaguer, it would be him. But he doesn't, which speaks well of someone who is a former All-Star but is not yet the superstar many had hoped he would become. He isn't a bust either. His career numbers -- 39 home runs, .727 OPS -- show he is somewhere in between.

At various times in his young career, Castro has gone from franchise savior to franchise killer, and he's experienced as much scrutiny in his career as most veterans. But he won't accept that he's faced undue scrutiny while playing for the most frustrated franchise in the game. Nobody so young should have has much pressure put upon him, but he's handled the attention relatively well.

"For me, it's not been a problem at all playing in Chicago, not for anyone I've seen really," Castro says. "Everybody has their support, and you have people here who watch your back, people who believe in you."

But for how long will they continue to believe?

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The general consensus on Castro is that he needs to improve his focus. That can be a dangerous characterization for a Latino player because a word like "focus" can be a loaded word often suggesting someone isn't intelligent. But in Castro's case, the description does seem to apply because everyone around him, Latino or not, believes that he could be one of the best players in the game if he could only eliminate some of the mental mistakes -- errant throws, defensive miscues, baserunning gaffes -- that have often plagued his career.

"He has a lot of talent," said Yankees outfielder and former Cub Alfonso Soriano, one of Castro's mentors. "I think he needs a little bit more concentration. I talked to him and told him he needs to focus just three or four hours a day to play the game and he'll be OK."

It seems impossible to believe but Castro, having just turned 24 in March, is already a veteran of almost four full seasons in the majors. He's so young that he's still younger than seven of the prospects on Baseball Prospectus' list of top 101 prospects. He's so young that he's only three days older than Chicago rookie outfielder Junior Lake. If he were in the minors, Castro would be considered one of the most promising talents in the game.

But based on merit, and partly on desperation by the Cubs, Castro made his major league debut  in 2010 at age 20, after only 264 minor league games. He posted an impressive .300 average and .755 OPS in 125 games during that rookie season.

"I thought I would come up eventually, but I never imagined that I would have come up as quickly as I did," Castro said. "I had to learn while developing at the same time."

The ensuing years have been a whirlwind: He became a cult figure favorite among Cubs fans as a rookie, he was an All-Star in 2012, and then he's been a cause of consternation ever since. And he's only 24, which seems to be the key number currently in Castro's career, not his batting average or his slugging percentage.

"I'm a completely different player than I was when I first came up," Castro says. "When one comes up for the first time you don't know anything. It's not the same baseball here that it is in the minor leagues. The game is faster, there are so many little things you don't know about the game when you come up. In the minor leagues you are playing to develop yourself as a player. When you come up here, the goal is to win. Those are things you gradually learn as time passes."

There is still a belief, although fleeting, that Castro can be the player to lead the franchise through this rebuilding. But he flopped badly last year with a .245 batting average and .631 OPS, and some doubt has crept up as to whether he can be a superstar or whether he will become just another failed Cubs prospect.

This season seems to be especially important for him. Careers aren't made or finished at age 24, but there does seem to be some urgency in regards to Castro's career on account of what happened last season.

"Those are things that I have in my mind because they happened, but I don't even want to talk about them anymore," Castro said. "I put them behind me. All of that has passed. It was a bad year, nothing that I was hoping for happened. There was a lot to think about, and I couldn't get it together. But you know, what happened last year has made me stronger because I had never gone through struggles like that. The next time things start to go badly, I'm better equipped to handle it because I have the experience of going through what I went through last year."

If he could only focus for three or four hours a day.

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The word "focus" seems to suggest an overwhelming concept, but it hardly needs to be so complicated. At the same time, focus has to come through work and desire.

"I don't know why people think it's an innate skill that can't be learned," said sports psychologist Dana Sinclair, who works with several major league teams. "It's not. Some people are more patient than others. It's a skill that if you learn to slow down and focus on execution, you can clean it up."

Sinclair added: "They have to understand their problem. A lot of people don't. It's usually a matter of calming down and breathing, settling down and pre-planning what they have to do."

By most accounts, Castro is not considered lazy, another-race driven characteristic that can be tagged on someone of color who lacks concentration.

"We've studied him a lot," first-year Cubs manager Rick Renteria said. "I think he's starting to actually learn how to play shortstop. He's been playing that position but he's just now learning how to play shortstop. It's a much more angular position. He was playing a lot more laterally, so he's been working really hard with [Cubs infield coach Gary Jones]. During practice he's really trying to b conscientious of the work he does. And he's been showing a lot of heart. He's been getting after it."

In order to improve his focus, Renteria said the Cubs are constantly engaging Castro in conversation during games. In between innings, a coach will approach and make sure that Castro is aware of what is going on. On the field, Renteria said a teammate might remind him of a game situation.

Second baseman Darwin Barney said he's noticed that Castro has developed a much more structured pregame routine. Such a thing can help a player concentrate better on the field because he no longer has to think of what he has to do prior to the game. It's one less thing to worry about on game day. It's the pre-planning that Sinclair referenced.

"I think his concentration has improved," Renteria said. "But like I said, the run of the season will give us a real indication of how he's done and how he's moving forward. You can't really base what a season is in a week. You have to give it a season. But are we moving in the right direction? I think so. I think he's staying more in tune with what's going on."

For so long Castro relied on pure athletic ability, but this is a new challenge. All the tools are there for him to be more focused on the game. It's simply a matter of desire. Will he be one of the faces in the Cubs clubhouse for a long time, beloved by fans, or will he be just another face that fades away?

"He's the one who has to bear the burden of being focused for nine innings," Renteria said. "The reality is that a major leaguer, a very successful major leaguer, will do that. And that's what he's striving to become."