Baseball's ever-isolating spotlight is one of the game's charming appeals. When the ball is pitched or when it is struck -- it's all on you, regardless of which glove you're wearing at the time, batting or fielding.

So, on a ball field, every man is an island. Except those two in the middle, whose teamwork is crucial as two pistons of the same engine, the most critical links in a strong chain.

There is a reason the base around which they operate is called the keystone. Why you can't separate shortstop and second baseman from the concept of double-play combination.

They're at the heart of the game's traditional up-the-middle requirement and have defined storied teams, from Tinker-Evers to Groat-Mazeroski to Trammell-Whitaker.

Now, middle infielders are also defining this new age of baseball mobility. The days of a Bill Russell and Davey Lopes anchoring an infield for a decade are gone.

Holding onto these positions is as difficult as holding your ground in the storm of a take-out slide. Second and short are among the first positions targeted by teams seeking to reach the next level.

All of which makes the Phillies' Jimmy Rollins and Chase Utley, and their National League East division, something special.

Reigning NL MVP Rollins and Utley will be entering their fourth full season as a tandem, perhaps pale by historical standards, but the Majors' longest ongoing partnership. Yankees shortstop Derek Jeter and second baseman Robinson Cano, together since a month into the 2005 season, are next.

Stability around the keystone is a hallmark of the NL East, where three of the other four teams could also have held-over combos. If Felipe Lopez holds off Cristian Guzman to start at short opposite Ronnie Belliard, the Nationals would join the Mets (Jose Reyes and Luis Castillo) and Marlins (Henley Ramirez and Dan Uggla) with incumbent tandems.

Only the Braves, who dealt shortstop Edgar Renteria to the Tigers and uncoupled him from second baseman Kelly Johnson, are certain of having a new starter around the bag.

Stay tuned

The Mariners also follow the trend. Yuniesky Betancourt and Jose Lopez will be starting their third season together and are signed through 2011 and 2010, respectively.

Middle Infielders

Remaining Schedule
On the other hand, five clubs are changing both halves of their double-play combo. The Orioles will become the sixth if they, as long rumored, deal second baseman Brian Roberts after having already moved shortstop Miguel Tejada in a trade with the Astros.

For those teams, Spring Training will be an intensive get-acquainted period, a time for new second basemen and shortstops to get on the same wavelength and page.

Twins manager Ron Gardenhire's choice at second -- Brendan Harris (acquired from the Rays as part of the Delmon Young package), Nick Punto or Alexi Casilla -- will be influenced by how new shortstop Adam Everett relates to them.

"A lot of it is going to be about compatibility," Gardenhire said. "We're going to have to wait and see how it all plays out with those guys together."

It's a long way from Spring Training to developing the sixth sense displayed by keystone soul brothers.

As the Phillies' Utley says of his vibes with Rollins, "We definitely feed off each other. It's a lot easier playing second with Jimmy over there. I always know where he's going to be."

For the first time in 17 years, Red Sox fans know familiar faces will be around the bag: Julio Lugo and Dustin Pedroia, the same guys who were there a year ago.

The defending World Series champs are set to open consecutive seasons with the same double-play combination for the first time since 1989-90, when Jody Reed was teaming with Marty Barrett (however, Reed and Luis Rivera did form Boston's primary combo 1990-92).

The real deal?

Three shortstops who may find their own 2007 splashes tough acts to follow:

• Troy Tulowitzki, Rockies -- Now that people know him, can he be as good with everyone watching?

• Orlando Cabrera, White Sox -- In his 11th season, he hit .300 for the first time, yet the Angels still dealt him away. Can he prove that was a mistake?

• Ryan Theriot, Cubs -- First he made Cesar Izturis disappear from the lineup, then he made him disappear from Chicago. Can the Cubs' fifth different Opening Day shortstop in as many years make himself at home?

And three second basemen:

• Asdrubal Cabrera, Indians -- May rank pretty low on the AL Cabrera totem pole (behind Miguel, Orlando, Melky, perhaps even Daniel), but the Tribe went 28-12 with him in the starting lineup.

• Aaron Hill, Blue Jays -- His offensive numbers increased across the board for a third straight season, and he topped MLB at the position in assists.

• Placido Polanco, Tigers -- Zero errors in 141 games ... good luck trying to top that.

Leading questions

David Eckstein has always hustled past his physical shortcomings, including limited range, but in Toronto, will he be quick enough to cope with the Rogers Centre turf?

Can San Diego shortstop Khalil Greene (27 homers and 97 RBIs in 153 games following two injury-filled seasons) stay healthy?

Can A's shortstop Bobby Crosby (213 missed games and five disabled list stints the last three seasons) get healthy?

Leading off

Those pepper pots playing in the middle of the infield also stir the pot from the top of the lineup. Last season, nearly half of Major League teams relied on either their shortstop or second baseman to lead off.

Revealing an interesting contrast in the two leagues' priorities, 10 of the middle-infield leadoff men were in the NL. Boston's Lugo, Baltimore's Roberts and, before his trade to the Mets, Minnesota's Luis Castillo were the only American Leaguers regularly used in the No. 1 slot.

Pop and polish

No question, had Baryshnikov picked up baseball, he doubtlessly would have played either short or second. The positions aren't played as much as they are performed, acts of athletic choreography best seen and appreciated through an action-freezing camera lens.

Cal Ripken Jr. and Roberto Alomar notwithstanding, short and second have always been defensive-minded positions. Saving runs is a higher priority than driving them in. Lusty hitting on top of clean fielding is quite a bonus.

Top six bonus babies of 2007, tandems with more home runs than errors:

• Rollins and Utley, Phillies +31 (52 HR, 21 E)
• Ramirez and Uggla, Marlins +24 (59, 35)
• Alex Gonzalez and Brandon Phillips, Reds +22 (46, 24)
• Rickie Weeks and J.J. Hardy, Brewers +16 (42, 26)
• Tulowitzki and Kazuo Matsui, Rockies +13 (28, 15)
• Khalil Greene and Marcus Giles, Padres + 13 (31, 18)

Keystone factoids

In the most recent survey for classifying free agents (Class A, Class B) which lumps third basemen, second basemen and shortstops, Texas' Michael Young ranked No. 1. In other words, Young rated ahead of guys like Alex Rodriguez, Tejada and Jeter.

The Reds' Phillips should have at least gotten the Bronze Medal. The NL fielding leader (.990, on eight errors in 782 chances) saw the Gold Glove go to Orlando Hudson, and, despite being history's second 30-30 second baseman, saw the Silver Slugger go to Utley.

Florida's Ramirez and Uggla combined to drive in 169 runs -- one fewer than the Yankees' Jeter and Cano, while combining for twice as many homers as the Bombers' duo.

Ramirez-Uggla also joined Jeter-Cano as the Majors' only DP combos to have both halves make 150-plus starts.

Young man's turf?

The oldest player on three teams' rosters will be playing in the middle -- second basemen Mark Grudzielanek of the Royals and Jeff Kent of the Dodgers and San Francisco shortstop Omar Vizquel.

Elias Sports Bureau special

Jeter (.604) owns the highest winning percentage among all active players who have played a minimum of 1,000 games. The Yanks have gone 1,104-729 since Jeter's debut in 1995.