Jennings, Brown lead group of rookies ready to take over in '11

Initially, the Giants elected to play it safe, signing the veteran, Bengie Molina, to a one-year contract while sending the rookie, Buster Posey, back to the minors for more seasoning. By mid-May, when it was clear that Posey belonged in the majors, the Giants promoted him to the bigs but played him almost exclusively at first base. By July, the rookie's impressive performance forced the Giants to trade Molina to the Rangers and install Posey behind the plate. By November, Posey was running out from behind the plate to be the first player to embrace closer Brian Wilson as the Giants celebrated their first World Series championship in 56 years and two weeks later won the NL Rookie of the Year award.

That the Giants were able to navigate the Molina-Posey conundrum so effectively last season was rare. Many teams don't have the luxury of re-signing veterans while holding off on promoting young players as talented as Posey, nor do those decisions often pay off with world championships. Every year teams must decide whether to re-sign often expensive veterans or hand their jobs over to rookies who are raw but talented, younger and, of course, cheaper. As the free-agent market slows down and spring training draw near, several teams will be replacing established veterans from 2010 with rookies in 2011. Here are six young players who could play vital roles for their respective teams in the season ahead.

Desmond Jennings, OF, Tampa Bay Rays

Replacing:Carl Crawford

Skinny: The departure of Crawford to the Red Sox opens a vacancy in leftfield that should eventually be filled by Jennings, a 23-year-old speedster who has been considered Crawford's heir apparent for a couple seasons. There's no guarantee that Jennings will be in leftfield on Opening Day for the defending AL East champions as they begin what's looking like a rebuilding year but, like Posey, Jennings should be the everyday starter before long. By all indications, Jennings has the potential to be Crawford-lite in 2011. He stole 37 bases at Triple-A, and is a .299 hitter with a .384 on-base percentage in five minor league seasons. His rare combination of quickness, plate awareness and terrific defense made him Baseball America's sixth-ranked prospect entering 2010.

Jennings won't be the only rookie asked to carry a heavy load for Tampa Bay in 2011. The trade of Matt Garza to the Cubs opens up a spot in the rotation for 23-year-old Jeremy Hellickson, who impressed during his brief stint in the majors last season, going 4-0 with a 2.05 ERA in his four starts.

Domonic Brown, OF, Philadelphia Phillies

Replacing:Jayson Werth

Skinny: If the Phillies didn't seem desperate to resign Werth, who inked a seven-year, $126 million deal with the Nationals, that's at least in part because 23-year-old Domonic Brown is waiting to take over for him in rightfield. At 6-5 and 200 pounds, Brown resembles a slimmer Ryan Howard, and he's been praised for his speed, power and throwing arm. He's proven that he can destroy minor league pitching, hitting .327 with 20 home runs and 68 RBIs in split time between Double-A and Triple-A in 2010.

Brown will need to learn plate discipline, but he should have plenty of time to mature in a lineup that's more than capable of waiting for him to develop. Given a month or two in the majors, he could pose a legitimate threat out of the five spot in Werth's absence. With Jimmy Rollins, Placido Polanco, Chase Utley and Howard hitting in front of him, Brown should get plenty of at-bats with men on base.

Martin Perez, P, Texas Rangers

Replacing:Cliff Lee

Skinny: Understandably, it's nearly impossible to replace Cliff Lee, who returned to the Phillies with a five-year, $120 million deal. In addition to his 2008 AL Cy Young award, he went 48-25 with a 2.98 ERA the past three seasons and is among the best postseason pitchers of his generation.

Perez, however, has the tools to make an impact. He has a terrific changeup, curveball and location for his fastball, he has the repertoire to be a dynamic starter. The 19-year-old Venezuelan is strikingly durable, totaling 214 2/3 innings over the past two seasons at Single A and Double A, giving him an asset Rangers co-owner Nolan Ryan clearly values. He's also lefthanded, allowing Texas to maintain balance in its rotation (C.J. Wilson is also lefty; Colby Lewis and Tommy Hunter are righthanded).

The problem is, at just 19 (he'll turn 20 in April), Perez is unpolished. He was roughed up in to the tune of a 5.96 ERA in 24 games at Double-A Frisco last year. his expedited stint to Double-A Frisco last year, carrying a 5.96 ERA. But he also averaged more than a strikeout per inning there, showing off a live arm that could be a big boost to the Rangers' rotation as they seek to defend their American League title.

Freddie Freeman, 1B, Atlanta Braves

Replacing: Derrek Lee

Skinny: Lee, acquired in an August trade from the Cubs, wasn't with the Braves for long but he did help them win the NL wild card. Atlanta let him walk as a free-agent (he signed with the Orioles) largely because they have Freeman ready to take his place. Freeman, 21, has hit 50 home runs in four minor league seasons, while batting .301/.363/.472. He also has a solid glove at first and got a taste of the majors during a late-season call-up to Atlanta. He doesn't have the skillset or the hype that teammate Jason Heyward, last year's highly-touted rookie outfielder, had when he arrived at spring training nor will he be expected to deliver from Opening Day the way Heyward was, but his combination of offense and defense could wind up being just as essential a part of their everyday lineup.

Tyler Matzek, P, Colorado Rockies

Replacing:Jeff Francis

Skinny: Colorado's staff is thin beyond Ubaldo Jimenez, and will only get thinner if Jeff Francis leaves via free agency. If the Rockies want to build off another late-season surge, they would be wise to consider promoting wunderkind Matzek, who blew away minor league hitters in 2010. He went 5-1 with a 2.92 ERA and 88 strikeouts at Class-A Asheville.

Though many scouts project that he won't crack the big leagues until 2012, Matzek has the stuff to contribute immediately. He has a fastball that touches 95 mph, a nasty slider, and curveball that began to come into its own as last season progressed. If all of his pitches are working, he should be able to silence many light-hitting National League lineups.

The Rockies may decide to keep the 20-year-old in Triple-A to start the season, but should the need arise for another starter during the season, look for Matzek to be the best option. Colorado's pitching staff possessed a 4.14 team ERA in 2010, a number that outpaced only the Cubs, Brewers, Diamondbacks and Pirates in the National League, and could greatly benefit from his presence if he continues to dazzle in spring training.

Mike Trout, OF, Los Angeles Angels

Replacing: Hideki Matsui.

Skinny: The Angels lost Matsui to the AL West rival A's and failed to sign Crawford, which could be a sign that they feel the best solution to their often lifeless offense is Trout. At 19 and in his first professional season 2010, Trout batted .362/.454/.526 and earned Midwest League Player of the Year honors. He also stole 56 bases and like Crawford, is valuable for his speed in the outfield. He would likely push Bobby Abreu into the DH slot upon his arrival in Anaheim, which could come by midseason. Trout is simply too fast and too talented to stay buried in the minor leagues for long.