Since the advent of Interleague Play, a player changing leagues is not so much the great unknown as it once was, since most veteran players these days have had at least some game experience against the other league beyond the usual Spring Training games.

And yet changing leagues still involves learning new pitchers (for position players) and facing hitters they haven't seen before or at least not very often (for pitchers), so moving to a new league remains in many ways the great unknown.

When the move to a new league involves a top player, the impact on his new team and league can take on even more significance.

Remember the winter of 2001, when a Japanese star named Ichiro Suzuki changed leagues to sign with Seattle and changed the Mariners' outfield picture?

What about Chris Carpenter? After spending the first six years of his career with Toronto, Carpenter was released by the Blue Jays in 2002, signed with St. Louis and after missing the 2003 season because of injury, joined the Cardinals in 2004 and was a big reason the Cardinals won the National League pennant that year.

Changing leagues cannot only change a player's career path, it can change the course of a season. Look what happened last winter.

Oakland went to the other league to sign right-hander Esteban Loaiza, who had been with Washington. Loaiza won 11 games for the A's and helped them to the AL West title.

Cincinnati dealt for right-hander Bronson Arroyo, who had emerged as a reliable starter during the previous two years with Boston. Arroyo won 14 games and led the NL with 240 2/3 innings pitched, helping greatly as the Reds contended in September for the first time in six years.

This season, another group of players will be changing leagues and perhaps changing pennant races.

Who will it be? The season will determine that.

Until then, here's a look at the most likely candidates:

Daisuke Matsuzaka, Boston Red Sox: The Red Sox have committed more than $100 million for Japan's best pitcher and the hero of the World Baseball Classic. Matsuzaka, who will join a rotation that is expected to include Curt Schilling, Josh Beckett, Jonathan Papelbon and Tim Wakefield, has already impacted the AL East race since the Yankees were among the bidders for the right-hander. If Matsuzaka is anything like he was in Japan, the Red Sox will get their money's worth.

Barry Zito, San Francisco Giants: Zito, who has never missed a start, moves across the bay to join a staff that finished 12th in the National League in team ERA last season and whose starters gave up more runs (540) than all but a half-dozen NL teams. The Giants used 21 different pitchers last season and lost their 2006 innings leader and best starter, Jason Schmidt, to the Los Angeles Dodgers. The lefty Zito is being counted on to step in and carry the lion's share of the load in '07.

Andy Pettitte, New York Yankees: The Yankees sought starting pitching this offseason, and with Pettitte's return following a three-year stint in the National League, the Yankees have plugged a potent lefty into the rotation. Pettitte is healthy again, and even with his injury problems he still made 83 starts during the last three seasons, just three fewer than he made his last three years in New York.

J.D. Drew, Boston Red Sox: After nine seasons in the NL, Drew moved on from the Dodgers to Boston -- though he and the Red Sox have not yet finalized his five-year contract. Yes, Drew has had as many as 500 at-bats in a season just once and has endured more than his share of injuries. But he has also put up impressive numbers -- a career .905 on-base plus slugging percentage -- and could put up even bigger numbers as the everyday right fielder in Fenway Park. Teaming his lefty bat with designated hitter David Ortiz and left fielder Manny Ramirez should give the Red Sox a formidable middle of the order.

Freddy Garcia, Philadelphia Phillies: The Phillies dealt for Garcia, 116-71 in eight seasons with the Mariners and White Sox, as part of their attempt to take the NL East with improved pitching. Garcia, winner of 31 games over the past two seasons, certainly should help in that regard, though here's a word of caution: he has allowed 58 homers in the past two years, and Citizens Bank Park is a home run haven.

Randy Johnson, Arizona Diamondbacks: Like Pettitte, Johnson returns to whence he came. The Big Unit wasn't a dominant pitcher during his two seasons with the Yankees, but he was their winningest pitcher during that time with 34 victories. The D-backs probably need more than Johnson every fifth day to contend for the NL West title, but, if he's healthy after having offseason back surgery, his presence certainly should have a big impact on the division.

Those six are the major movers to watch this year. But there are others who might also be shaking things up in a new league, including:

Ted Lilly, Chicago Cubs: Lilly actually broke into the Majors in the NL, making three starts for Montreal in 1999, but he was dealt soon after to the Yankees and spent the last seven years in the AL with New York, Oakland and Toronto. The southpaw has averaged 170-plus innings and 12.2 wins over the past four seasons.

Adam Kennedy, St. Louis Cardinals: The second baseman is reunited with shortstop David Eckstein, his double-play partner with the 2002 World Series-champion Angels.

Mike Piazza, Oakland A's: Piazza, the all-time home run leader by a catcher, takes over the DH spot vacated by Frank Thomas. Piazza has spent his entire career in the NL, with the Dodgers, Marlins, Mets and Padres.

Eric Gagne, Texas Rangers: If the former Dodgers All-Star closer and 2003 NL Cy Young Award winner is healthy, the Rangers could have a dominating closer and perhaps the best bargain of the offseason.

Mark DeRosa, Chicago Cubs: It will be hard to repeat a career year, but DeRosa, who moves over from Texas, should at least put a stop to the revolving door at second base.

Bengie Molina, San Francisco Giants: Molina set career highs with 19 homers and 202 total bases last season. After nine years in the AL with the Angels and Blue Jays, Molina is ready to fill in nicely for the injured Mike Matheny.

Josh Barfield, Cleveland Indians: The second baseman broke in with the Padres with high regard and had a promising but inconsistent rookie season. He'll fill a big hole for the Indians, who dealt away Ronnie Belliard last season.

Kei Igawa, New York Yankees: A lefty strikeout artist who is only 27 years old, Igawa tied for the Japan Central League lead in strikeouts last season while finishing in the top seven in wins, innings, ERA and complete games.

Finally, a "welcome back" to two who return to the leagues from which they were dealt last summer:

Aubrey Huff, Baltimore Orioles: A versatile player with some power who spent nearly seven seasons with Tampa Bay before being dealt to the Astros last summer, the left-handed batting Huff should provide much-needed protection for Miguel Tejada.

Carlos Lee, Houston Astros: Lee is certainly no stranger to the NL, where he played for nearly two seasons before Milwaukee dealt him to the Rangers last July. He spent the first six years of his career in the AL with the White Sox. Lee gives protection for Lance Berkman and should provide an immediate boost to an offense that finished last in the league in hitting last season and next to last in total bases, slugging and hits.