As the Tampa Bay Rays and Philadelphia Phillies prepare to slug it out in the World Series, a baseball contest of a different sort—involving some of the sport's tiniest players—is raging around America's suburban fields.

At the center of the tug-of-war: children's baseball uniforms.

On one side is Major League Baseball, which has been asserting its trademark rights and collecting licensing fees through an official uniform supplier, Majestic Athletic, Ltd. M.L.B. has threatened legal action against vendors who put pro team names on jerseys worn by Little League and amateur players without permission.

On the other side, some youth leagues are crying foul. They denounce the higher cost of official uniforms as well as what they feel are M.L.B.'s hardball tactics to force them to buy from a single supplier. So some are boycotting pro team names.

In Santa Clarita, California, a city north of Los Angeles, the William S. Hart league's
 baseball division narrowly voted to continue using names like the Mets and
 the Orioles. Its 1,800 players will still wear official hats bearing 
team logos, but the league plans to drop all pro names from team jerseys, to avoid M.L.B.-licensed apparel.

Others have kicked the Major League off the field altogether, switching to generic collegiate monikers like Trojans and Bruins, or looking to the rainbow. In Bloomingdale, Illinois, where miniature Pirates and Marlins once faced off, teams are now identified by color.

"At first the younger kids were disappointed...but you're saving the membership thousands of dollars," says Rick Palandri, a board member of Bloomingdale Baseball and Softball Association. The league's moisture-wicking jerseys—imperative, Palandri says, for keeping boys and girls cool in summer—cost about half the price of comparable M.L.B.-licensed outfits.

Out of more than 10,000 youth-baseball leagues across America, about 4,000 wear M.L.B.-licensed uniforms. No one knows how many use pro-team names but avoid their mention on jerseys, or copy on the sly—like one in California rumored to import knockoffs from Mexico.

To police sales, M.L.B. has been sending warning letters to small vendors and making them sign agreements prohibiting the use of its team names in any form, even without official logos, on the athletic apparel they sell.

"Major League Baseball is creating a monopoly for its products," says Fred Miller, vice president of Evans TeamWear, an Orange County company that provides uniforms to more than 100 youth leagues in California and Nevada.

Evans recently paid M.L.B. a $75,000 settlement over unpaid royalties after being contacted by M.L.B. lawyers—though Miller says his company did nothing wrong. "It comes down to a business decision," he said. "Do I want to fight this in court for [a lot more], or pay the settlement fee now?"

But pro-baseball officials say they must protect their trademarks as a matter of law. In 2005, M.L.B. entered into a licensing arrangement designating Majestic, an apparel manufacturer in Bangor, Pennsylvania, as the exclusive supplier of all uniforms bearing its team names—from pros in the Major Leagues to kids in Little League and casual fans everywhere.

"We're obligated by our contracts," said Matt Bourne, spokesman for M.L.B., the corporate entity representing the 30 pro-baseball clubs. "If you don't protect your intellectual property, there's a risk of losing ownership. Team names are our identity. It's critical to the brand names we've built for more than 100 years."

It's also big business. The Sporting Goods Manufacturers Association said the retail value of all Major League Baseball-licensed merchandise—including uniforms and memorabilia—totaled $3.3 billion last year, the highest for any professional sport.

Neither M.L.B. nor Majestic would discuss the specifics of their contract. But in public statements, Majestic's parent corporation, VF Corp.—the world's largest apparel company, which also owns Wrangler jeans, Vans footwear, North Face outerwear, and Nautica sportswear—touts its booming "Major League Baseball business under the Majestic brand."

In 2007, the year VF acquired Majestic from its founding family, Majestic produced $156 million in sales. The brand accounted for another $33 million jump in revenues for VF in the first half of 2008, according to recent Securities and Exchange Commission filings.

Licensing fees from Majestic, in turn, help boost pro baseball's bottom line. M.L.B.'s total revenues—which includes ticket sales, television deals, and online subscriptions—surged to a record $6.1 billion in 2007 from $3.4 billion in 2000. Over the same period, licensing revenues more than doubled, although M.L.B. declined to reveal specific figures.

Despite its business success, some say pro baseball may be wiser not to be so aggressive in squeezing money from its youngest enthusiasts.

"It alienates everyone involved," says John Skilton, who runs Baseball-Links.com, a repository of more than 12,000 websites and blogs. "With its labor conflicts and the steroid controversy...it's one more in a series of black eyes for them."

If the team-name tussle ever winds up in court, legal analysts say it's unclear which side would win. The law generally protects a trademark only if an unauthorized use is likely to cause confusion—that "people would think Major League Baseball was somehow associated with the production of this uniform" when in fact it wasn't, says Charles McManis, a professor at Washington University School of Law.

If youth leagues take steps to differentiate their apparel, a court could rule against M.L.B., reasoning that "all people will think when they see the jersey is, Oh yeah, they're just making their jerseys look like Dodgers jerseys."

But if a court finds a team name to be a "famous mark"—which enjoys more legal protection against dilution in the marketplace—M.L.B. would probably prevail. The key is whether the name is distinctive and well known enough to constitute a "famous mark," says McManis, author of two books on intellectual-property law.

That decision, however, would not necessarily cover all Major League franchises, experts said. A court could deem White Sox and Yankees distinctive enough to be "famous marks," but not more generic-sounding teams like the Tigers and Indians.

In the court of public opinion though, M.L.B. has been striking out. Its stance has been barraged with boos and hisses in the blogosphere. Comedian Stephen Colbert has also been piling on.

"These kids aren't just stealing team names—they're ripping off all kinds of stuff from the Majors," Colbert deadpanned on a recent show. "Where did these kids get the idea of using a mitt?" he said. "Or wearing a cup?"

In its defense, Major League Baseball notes that it spent $30 million on youth programs in the last five years and makes sure that Majestic, in addition to its regular ware, offers a low-price, royalty-free line of uniforms. Cultivating a good relationship with children "is obviously very important to us," says Bourne.

Some believe pro baseball needs to do more to court the young. After all, they're the ones who one day will decide whether to shell out—or not—for tickets, hotdogs, jackets, and souvenirs.

"M.L.B. should be paying the kids to wear its uniforms," says Palandri, the Bloomingdale board member. "It's free advertising for them."