KANSAS CITY, Mo. � If Red Sox coaches and executives thought they had a good grasp on the trajectory of player development and the transition of young players into the major leagues, this season has delivered a jarring reminder of how little they rea

KANSAS CITY, Mo. � If Red Sox coaches and executives thought they had a good grasp on the trajectory of player development and the transition of young players into the major leagues, this season has delivered a jarring reminder of how little they really know.

And it�s not just the Red Sox, either.

The dominant theme of this season in Boston has been one of the dominant themes across baseball. Highly touted young players have come to the major leagues with enormous expectations � perhaps unfair expectations � and stumbled badly.

Will Middlebrooks looks overmatched and overwhelmed at the plate. So too does Jackie Bradley Jr., who threw his bat after a strikeout Friday night. Xander Bogaerts started strong but saw his numbers nosedive, hitting under .150 over a span lasting almost three months � and he was supposed to be the best of the bunch.

But it�s hardly a problem unique to Boston, even if perception has intertwined its reliance on youngsters and its last-place trajectory. Chicago�s Mike Olt, Houston�s Jon Singleton, Pittsburgh�s Gregory Polanco, St. Louis� Oscar Taveras � all have come to the major leagues with great expectations, and all have flopped thus far.

The Kansas City Royals have spent years contending with just this problem, cultivating a well-regarded farm system only to see their highly touted prospects fall flat upon reaching the major leagues.

Left fielder Alex Gordon took four years to blossom into the MVP-caliber player he has become, including a detour back to the minor leagues late in his fourth season in the major leagues. Designated hitter Billy Butler was a below-average hitter in his second season in the major leagues before something clicked for him. First baseman Eric Hosmer has hit just seven home runs. Third baseman Mike Moustakas was shipped back to Triple-A Omaha earlier this season.

Those growing pains contributed to four straight 90-loss seasons, part of an interminable stretch of irrelevance, but the Royals� patience with their young players also has contributed to the first September pennant race at Kauffman Stadium in a generation.

�There�s no way to fully predict how a player is going to perform until they go up here and do it,� Royals general manager Dayton Moore said in an interview this weekend. �George Brett got sent down. Alex Gordon got sent down. You can go on and on with the players that have failed initially at the major-league level.�

AS ANALYSIS AND DISCUSSIONS of prospects has increased in recent years, so too has the expectation that those prospects will make an immediate impact at the major-league level.

No one batted an eye when the Red Sox entered this season relying heavily on a trio of relatively unproven young hitters in Bogaerts, Bradley and Middlebrooks. All three had hit at every level of the minor leagues. Nobody had any reason to believe any of them would fail to hit in the major leagues.

The statistics a hitter compiles in the minor leagues, however, only have so much to do with the success he�ll have in the major leagues. Player development is neither linear nor inevitable. The deciding factor might not be evident on the back of any baseball card � or on any breakdown of swing path or fastball command.

�The main variable to it all is the mental side of the game,� said Red Sox manager John Farrell, who spent six years as the director of player development in Cleveland. �Getting to know the player is probably the most important thing � or, at least, it�s equally important to know the person as evaluating the tools.�

Bogaerts, Bradley and Middlebrooks all cruised through the minor leagues, pummeling opposing pitching at every level. Success certainly begets success � a player who hits .200 in Triple-A isn�t likely to thrive in the major leagues � but a hitter who never fails in the minor leagues will wind up confronting failure for the first time in the major leagues.

That presents a daunting test of mental fortitude, something some players handle better than others.

�Most of these players are dealing with failure at the first time at this level,� Farrell said. �It�s a lifelong pursuit to get here. Is it a huge letdown and disappointment? There are going to be some personalities that adapt to it more readily than others.�

�Even if a player gets off to a really good start, you know he�s still going to have some ups and downs,� Moore said. �Until that player goes through those struggles and gets through that, they�re not battle-tested. Once they go through that tough period and they come out of that OK, you get a better feel for that.�

Defensive shifts, video work and ubiquitous mid-90s velocity has suppressed offense across the game, and that only makes it more difficult to get to the plateau that allows a hitter to feel good about himself.

�Inevitably, a player is attached to the end result,� Farrell said. �As much as we can say to focus on the process, that sounds all well and good � and there�s a lot of merit to do that because you can�t control everything � but at some point you need some positive return for the work you�re putting in.�

And while teams can simulate plenty else in the minor leagues to prepare their players for the highest level, there�s no simulating the speed, challenges, pressures and distractions they face when they get there.

�There�s no replicating this environment,� Farrell said.

�There�s no model you can create in the minor leagues that is going to predict exactly how they�re going to do when you get them on the big stage,� Moore said, �especially a place like Boston, where there�s so much intensity and media and fans. It�s a huge stage. It�s a national stage.�

IF THE WAY YOUNG PLAYERS handle the valleys dictates their eventual success or failure, the seemingly inconsistent treatment of those young players when they do encounter struggles makes far more sense.

Middlebrooks has spent extended time in the minor leagues in each of the last two seasons. Bradley spent almost three weeks in the minor leagues in August and September before being recalled. Bogaerts, on the other hand, kept right on playing every day even as he was hitting at a level more reminiscent of a National League pitcher than the next Nomar Garciaparra or Hanley Ramirez.

For a team, the evaluation of the player goes far beyond the numbers or even the quality of contact. The evaluation has to include a look at the way the player has handled the failure when it has come, the extent to which it has his undermined confidence or eroded his motivation to show up and work every day � and assessing a player�s makeup can be far more difficult than assessing his bat speed.

Boston stuck steadfastly with Dustin Pedroia as he struggled through his first month in 2007, which makes sense in retrospect given what we all now know about his determination and makeup. The way the Red Sox have repeatedly praised the maturity and poise of Bogaerts indicates they view him similarly.

�That�s where you look past the numbers in the moment and you gauge that by your interactions,� said Farrell, not speaking about any player in particular. �How are they handling the failure? How is their body language? The responses to questions tell you where that player is at.�

�A lot of it comes back to how much a player really loves to play,� Moore said. �A lot of guys think they do, but when they�ve got to show up every single day, it becomes more of a grind to them � and when it becomes a grind and you�re just trying to get through it, you can�t be successful.�

In a counterintuitive way, perhaps the hitters best equipped to succeed in the major leagues are the hitters who don�t hit .300 at every level � or at least have confronted adversity along the way, something top prospects don�t see until the major leagues.

�Typically, the guys that surprise you are the guys that have maybe struggled more in the minor leagues than other guys,� Farrell said. �Those are where the surprises come from. They�ve dealt with failure. If they�re scuffling a little bit, they�re saying, �It�s no big deal. I�ve been here before.��

If the Red Sox take a lesson away from this season, it might be the tremendous risk that comes with incorporating three unproven youngsters into a major-league lineup at the same time � especially in a high-profile market like Boston.

The task of transitioning into the major leagues represents a tremendous physical challenge for every young player, a challenge unlike any he has ever experienced. The mental challenge might dwarf it.

�The greatest challenge for every player is not the opponent,� Farrell said. �It�s himself.�