A schedule changeup floating through its second decade as a presence in baseball's summer months, Interleague Play has gone from a novelty that bucked longstanding tradition to something of a tradition in its own right.

For the decades before its debut on June 12, 1997, the games that involved both American League and National League players were known as, in their annual order, the All-Star Game and the World Series.

That was it.

Miracle Whip

Then came Interleague Play, which was intended to help boost attendance, to bring together regional and intracity rivals during the regular season, and generally to provide an annual change of schedule scenery on Major League Baseball's marathon trip through summer.

All those missions have been accomplished, most anyone would agree. But Interleague Play wasn't universally accepted when it began by crossing a line never crossed before, and not everyone is enamored with it even now, whether over scheduling issues or a nostalgia for the days of two fully separate leagues that crossed paths only for two marquee events. But it has become part of Major League Baseball's DNA, with thousands of games contested, countless memories collected and a segment of the schedule that every year spurs both interest and debate about its merits.

One thing seems clear: Interleague Play isn't going away any time soon.

"As long as I'm here, we will have Interleague Play," Commissioner Bud Selig said succinctly following an owners' meeting last year. "I love it."

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While Interleague Play will presumably remain in place well beyond Selig's contract through 2012, some have called for a study into how Interleague Play operates from year to year, and possible adjustments that could be made to limit its impact on races for postseason spots. The Special Committee for On-Field Matters formed by Selig last year has Interleague Play on its agenda, and one member of that group suggested recently that there is some room for improvement in what generally has been consumed as a successful side dish to the overall menu that is the regular season.

Toronto Blue Jays president and CEO Paul Beeston, one of four club executives on the 14-member special committee and the former president and chief operating officer of Major League Baseball from 1997-2002, suggested recently that perhaps Interleague Play has become a little too much of a good thing.

"I think there's always some place for Interleague Play," Beeston told the Canadian Press earlier this month. "Whether the number should be 18 games or not, I'm not 100-percent certain. ... Do you go to six, do you go to nine, do you go to 12, do you go to 15? I think you can make a case for all of them."

Another issue inherent to the changeup Interleague Play throws the schedule: The rotation of division foes from year to year provides varying degrees of competitive balance in a given season. That was the case during the first five years, when it was broken down to region (East vs. East, etc.) and has remained a bone of contention, as it were, as divisions have rotated to play other divisions since 2002.

This year's Exhibit A is the two-time defending National League champion Phillies. They play four contenders in the Red Sox (six meetings), Yankees, Twins and Blue Jays during their 18-game foray into 2010 Interleague Play, as rough a stretch as any team must contend with. The rest of the NL East has it tough as well, NL Central contenders St. Louis and Cincinnati might have it a little easier, and teams like the Dodgers have six tough games against their rivals.

"I've been complaining for years, but the only thing I say now is that it should be fair," said Dodgers manager Joe Torre, also a member of the Commissioner's special committee. "I don't know how we can make it fair. When you play different teams than other teams in your division, it's not fair. We play a contending team [the Angels] six times. Some teams play teams that are not contending teams. I just think in terms of fairness, give everybody the same shot against the same caliber of team you're playing."

And, of course, there is the bat-wielding gorilla in the room: the designated hitter, the biggest difference between the two leagues. The standard for Interleague Play has remained that the DH is employed in American League parks but not in National League parks, just as is the case for the World Series and, until this year, the All-Star Game. Beginning July 13 in Anaheim, the Midsummer Classic is going to include the DH every year, regardless of the site.

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In terms of its original mission, Interleague Play generally has been considered a success. More than 100 million fans have attended Interleague games, and annual average attendance figures have hovered near its overall average of 33,245 per date. That represents a boost over full-season averages during a string of the highest overall attendance marks in MLB history. For instance, the fifth-largest attendance total of 73,418,479 in 2009 showed an average of 30,226, while the Interleague Play average over 251 dates was 33,351.

"I initially talked about eliminating it," said Torre. "Then you realize you can't. Put all the numbers together, and it draws people to the ballpark. If that's the case, I back off. I understand that if you're keeping up with supply and demand, bite your tongue."

Also, rivalries such as Yankees-Mets and Angels-Dodgers have played out in the regular season, bringing their own dash of flavor to each city. However, not all of the matchups considered traditional rivalries for the sake of Interleague Play ring so true, and, as Torre suggested, six games might be more than even the top rivals need to play against each other.

As a whole, the short annual foray into Interleague Play generally gets positive reviews from those involved in playing the games.

"I think baseball got more interesting when they started doing Interleague," said Reds shortstop Orlando Cabrera, who has split his 14 seasons between the two leagues. "Guys have a chance to interact with everybody, all the players, and go to every stadium. And fans have the chance to see everybody."

Even if that exercise changes up the pattern of the rest of the schedule? Sure, says Mets outfielder Jason Bay.

"Stuff like that only happens a couple times a year," Bay said as he made his first Subway Series appearance this season. "It changes up the same series-after-series routine. It's nice to have that every now and then."

In its lifetime of 14 years and counting, Interleague Play has fostered true moments of glory. Some of the bigger moments:

• The Astros used a record six pitchers to throw a no-hitter at Yankee Stadium on June 11, 2003.

• Tigers ace Justin Verlander no-hit the Brewers on June 12, 2007, one year after winning AL Rookie of the Year honors.

• Roger Clemens earned his 300th victory pitching for the Yankees against the Cardinals; Sammy Sosa joined the 600-homer club with the Rangers against his former club, the Cubs; and last year, the Yankees' Mariano Rivera reached the 500-save plateau against the Mets.

• A number of players have made returns to former home ballparks that they might not have otherwise, but nothing compares to Ken Griffey Jr.'s emotional hugfest in Seattle in 2007.

"Never could I imagine that it would be like this coming back," Griffey told the capacity crowd that jammed into Safeco Field for "Welcome Home Junior" night.

It could be said in Griffey's case that Interleague Play became very much a part of baseball's larger story, an impetus for a superstar player to realize he could go home again, as Griffey did in 2009, returning to Seattle.

Then there was this summer's return of the year, Manny Ramirez's appearance at Fenway Park for the first time since joining the Dodgers. It was an episode of "The Return of Manny Being Manny" that might have occurred in the World Series, but certainly wasn't as guaranteed as the days on the June 2010 schedule.

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When it began with Rangers left-hander Darren Oliver pitching to Giants leadoff man Darryl Hamilton, who delivered a leadoff single, four NL West-AL West matchups started off what has turned into more than 3,000 games between NL and AL opponents. The AL had a 138-114 winning margin in 2009, giving the AL a sixth consecutive year with the edge over the NL, including an all-time overwhelming margin of 149-103 in 2008. Including the NL's 22-20 advantage through the first weekend of Interleague games in May, the all-time series stands at 1,694-1,556 (.521) in favor of the Junior Circuit.

Where does Interleague Play go from here?

Altering the schedule is one idea. Another one that has been floated in years past is adjusting how the DH is used, perhaps using it in NL parks instead of AL ones.

Says Dodgers utility player Jamey Carroll: "That way, NL fans get to see the DHs, and AL fans get to see what the NL-style is about."

That concept is the very essence of the exercise, after all: Baseball's fraternal twins, taking an annual walk in each other's shoes, for all to see.

Interleague Play is about baseball's two leagues intertwining for a couple of weeks each season, and it forges ahead through another decade with undeniable imperfections, but also a role in building Major League tradition year by year.