For years, Orioles fans have had an almost primitive response to being outnumbered in their own stadium by thousands of visiting fans who root, root, root for the Red Sox or Yankees. To the home fans, it is as if invaders are threatening the castle.

Later this month, the Orioles will host the Yankees and Red Sox. Yankees fans will sport "Jeter" jerseys, and Boston backers will wear "Ortiz" jerseys and chant "Let's go Red Sox!" Feeling protective of their territory, Orioles fans will want to remind them that this is Camden Yards, hon, not Fenway Park.

It all begs the question: Is there anything that Baltimore or the neighboring Washington Nationals can do about the indignity of having their respective backers overwhelmed by road-tripping spectators cheering for the Red Sox or Yankees in Baltimore, or the Phillies in Washington?

A partial answer looms this weekend. With Philadelphia playing in Washington for a three-game series, the Nationals are trying out a new, "Take Back the Park" marketing and ticket-sales strategy designed to prevent their stadium from turning into a southern extension of Philadelphia's Citizens Bank Park.

The Nationals held a pre-sale for the series in February and March open only to fans with credit cards linked to addresses in Washington, Maryland and Virginia. "We don't release ticket sales numbers, but I can tell you that this is the most successful pre-sale we've had," Nationals chief operating officer Andy Feffer said. The club also offered two free tickets for later games to fans who bought two seats for this weekend.

"We created this campaign because we felt very strongly that we needed to do something about the Phillies fans who inundated Nationals Park over the last few years for our games," Feffer said.

It's a strategy the Orioles are certain to notice. Later in the season, Baltimore hosts the Yankees and Red Sox for weekend series. The weekends are when most visiting fans tend to descend on Camden Yards — sometimes by the bus load.

The influx of thousands of interlopers is "an issue we've faced since the mid '90s when the Red Sox and Yankees started to get good again," said Orioles spokesman Greg Bader. "It is unfortunate that that happens."

While the Orioles have no plans for Nationals-style pre-sales, "we do not and never have marketed to Red Sox and Yankee fans," Bader said.

Not all of the visiting-team fans are from out of town. Some live in the Baltimore-Washington region.

"We would prefer that 46,000 seats were sold only to O's fans," Bader said. "Short of that, we don't want to be sitting on unused inventory. (Having) no fan does nobody any good. It hurts us and the surrounding tourism industry."

Washington fans feel Baltimore's pain.

"I find it very unpleasant to have to endure (Philadelphia's) barbaric fans who pride themselves in being not only uncivilized, but downright vile," said Barb Angelino, a Washington fan. "I love the idea that the Nationals are making an effort to keep the attendance of Phillies fans at a minimum."

There were many more Nationals fans than Phillies fans in the stadium as this weekend's series began. The Philadelphia fans were noticeable — they began rhythmic applause Friday night when the Phillies tried to rally — but were not as big a presence as in recent years. On Saturday, too, there were more Nationals fans than Phillies fans.

Scenes from past years motivated the Nationals to act. In Washington's 2010 home opener, Phillies fans booed Nationals players during pregame introductions before beating the Nationals , 11-1. "They booed (Washington third-baseman) Ryan Zimmerman getting the Silver Slugger award," said season-ticket holder Chris Alvord. "A lot of the (Nationals) fans who were there swore never again to go to a Phillies series."

After a Nationals victory last season, "a Phillies fan, who I had never seen or spoken with before in my life, got right up in my face and said to me 'What are you so happy about? You're 20 games out of first place', " said Nationals fan Ray Mitten. "This is a mild story of what others have put up with."

Feffer said he hopes the "Take Back the Park" campaign will "ignite a rivalry between two teams only two-and-a-half hours apart" but that fans will remain civil in the stands.

"We expect a fan-friendly environment for all visitors to enjoy the game," he said.

The Nationals will host another Phillies series later in the season. "The best way to eliminate Phillies fans coming down is for the Nats to beat the Phillies," Mitten said.

jeff.barker@baltsun.com

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