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2/25/2013 11:00 A.M. ET

Freshman phenoms wary of sophomore slump

A year ago at this time, baseball fans knew the names -- Bryce Harper, Mike Trout, Yoenis Cespedes, Yu Darvish -- but there was no knowing how those players would affect the game in their rookie seasons.

Fast forward to today. We're all a year wiser, those players are a year more experienced, and the game is better off for it.

Harper broke into the National League, setting unprecedented marks for a teenage player en route to the league's Rookie of the Year honor over Arizona standout Wade Miley. Trout led American League rookies in practically every offensive category, challenging Miguel Cabrera and his Triple Crown for the league MVP, but "settling" for a unanimous Rookie of the Year ballot instead.

Cespedes wowed fans on the West Coast with his arm and big bat. Darvish won 10 games before July and finished with 16. Miley, too, won 16 games and turned in a workmanlike 194 2/3 innings. Todd Frazier was a force at third base in Cincinnati, and Norichika Aoki finished his season in a Brewers uniform on a tear, batting .306 with 18 RBIs in September and October.

So here we are, preparing to see these players take the field, no longer as rookies, wondering … What do they have in store for us as an encore?

"It's my second year in the big leagues," Harper said. "I'm not going to do anything different -- just play my game. I have a great team, a great group of guys around me that help me play every single day. It's going to be a lot of fun. I'm excited to get this season started."

If Harper and Trout can avoid any sort of sophomore slump and turn in seasons comparable with last year, we'll be in for a treat. Coincidentally, they each played 139 games after being called up to the big leagues after Opening Day, and both should have full years on the horizon.

"I have no doubt that Mike will very easily handle his transition," Angels general manager Jerry Dipoto said. "Like with any player, there will be adjustments, just like there were in Year 1 for him. He'll make them. He makes them day to day, inning to inning and month to month, and I don't necessarily think year to year is going to present an emotional challenge for him."

It's typical for young players to hit lulls -- if not in their rookie season then sometimes in their second year. Many of the aforementioned players experienced it last year.

Harper hit 307/.390/.553 in his first 40 games before running into a slump his next 55, when his slash line came in at .204/.273/.290. After hitting a remarkable .361 from May to July, Trout hit .287 from August to October. Darvish went 3-5 from July to August.

It's not just the players possibly running into a wall, but the league making the appropriate adjustments. Veteran hitters, after seeing a young pitcher once or twice, know to adjust. The same goes for pitchers facing such young players as Harper, Trout, Aoki and Frazier. So it's all about how the young players counteract those adjustments.

"I'm going to put [in] all my emphasis, and I'm going to do everything I can do to be the best behind the plate," Rockies catcher Wilin Rosario said of his second-year improvements. "It's a matter of time. Remember that I told you that. You'll see what's going to happen."

Rosario set a Rockies rookie record with 28 homers and led NL newbies in homers, RBIs (71) and slugging percentage (.530). According to STATS Inc., he was the fourth rookie catcher age 23 or younger to hit at least 20 homers in a season.

But he also led the Majors in passed balls (21) while serving as the primary catcher for a staff that led the big leagues with 94 wild pitches.

Harper, too, will have adjustments to make. After making almost all of his defensive appearances last year in either center or right field, he's expected to play left field this year, and that will help keep him on his toes.

"I don't think you should ever be comfortable," he said. "Every single time you go into Spring Training, someone can come up here and have a great spring and possibly take your spot. I've always thought that, and I think you should work hard every single spring, work hard during the season, try and get better every single day out here, try and progress in outfield, hitting, baserunning, anything you can."

Joey Nowak is a reporter for MLB.com. Follow him on Twitter at @joeynowak.‬ This story was not subject to the approval of Major League Baseball or its clubs.