On a sunny fall day in Locust Point, neighborhood residents are out in force. Toddlers frolic in Latrobe Park's playground as tennis players trade volleys on a nearby court. Joggers thread through narrow streets lined with Formstone facades and renovated rowhouses with rooftop decks, while bicyclists pedal along the waterfront promenade outside Under Armour's Tide Point office complex.

Under Armour may be a $1 billion company that sells its sports apparel around the world, but home is Locust Point, be it ever so humble. And there lies a potential conflict.

The company has announced plans to double the size of its physical plant — news that upset some residents of the 1,800-home neighborhood on the narrow peninsula. They worry about construction that could block views, congestion that could add to parking woes, and competition from new shops and restaurants that could hurt longtime businesses.

"Everyone realizes Under Armour is a great company," said Christopher Ritsch, president of the Locust Point Civic Association. "But that doesn't mean they get to do anything they want at the expense of the community."

"We live here. This is our home. We do not want to be Fells Point. We do not want to be Federal Hill."

Under Armour maintains expansion is crucial to its future success. And its success is crucial to Locust Point, company officials say, because Under Armour creates jobs.

"This is not like we've dropped in here and are developing something just to maximize our square footage," J. Scott Plank, executive vice president of business development, said of the 15-year-old company's plans to grow. "If we don't have the ability to expand, the jobs will go somewhere else."

At a time when many companies are reluctant to hire or are shedding workers, Under Armour anticipates it will need to double the size of its headquarters over the next few years to meet demand for its products.

The company, which employs nearly 1,200 people at its Tide Point headquarters, has added about 400 workers in the past five years and plans to add as many as 300 next year. In addition to office space for the additional employees, Under Armour says it needs room for a flagship store to showcase its merchandise, and athletic fields that could be used for testing products and holding tournaments.

The company also plans several waterfront improvements that it says will benefit the entire neighborhood, including a hiking/biking "greenway" linking the neighborhood to Fort McHenry.

A request to allow the addition of as much as 400,000 square feet of office space and 50,000 square feet of retail is expected to come before the City Council in December.

In its first phase of expansion, Under Armour plans a four-story building to house offices and a 20,000-square-foot flagship store. The company hopes to begin construction next year and complete it in 2013.

The company plans to continue building as its business grows, but has offered no definite timeline. In a later phase, the Tide Building in the complex could be razed and replaced with a larger structure, plans show.

Community members, who have formed a task force to work with Under Armour, say they simply want a chance to be heard as the plans develop.

"Under Armour is a great brand to have locally," said Jeffrey W. Link, 34, a financial adviser who has lived in Locust Point since 2003. "It's great for property values. There's a lot of good to it, as long as [the company] works with the community and not against the community."

Life in Locust Point has changed before.

It has been decades since local residents were able to walk to work at nearby factories — including Procter & Gamble at what is now Tide Point. Neighborhood mainstay Domino Sugar remains, but many of the area's industrial employers have long since closed.

When Dan Macatee opened Hull Street Blues Cafe 27 years ago on the site of a former 19th-century saloon, his customers were likely to work in blue-collar jobs in the neighborhood.

"No one knew where Locust Point was, and a lot of people liked it that way," he said. "We still have a lot of the people who've been here for generations and are used to their own little hideaway."

With the decline of manufacturing jobs, office workers from Tide Point and Under Armour have helped business, Macatee said. By 5 p.m. on a recent weeknight, several employees of a nearby architectural firm were settling in at the bar for happy-hour drink specials, while others headed to the cafe's nautical-theme dining area, where crab cakes and shrimp dishes are served.

Macatee hopes that Under Armour's expansion will give a boost to business, but he can't help but worry about what additional traffic — and potential restaurant competitors — might mean.

Some of the area's newer residents have moved into condominiums at Silo Point, a redeveloped grain elevator at one end of Beason Street. Nearly two-thirds of the condos have been sold, including a few to Under Armour employees who wanted to live within walking distance of work, said the project's developer, Patrick Turner.

Those Under Armour workers are among about 80 who now live in the neighborhood and more than 100 others who live in the South Baltimore area, the company says.

Turner has leased all of Silo Point's retail space, and he expects the final tenant, a gourmet deli, to open soon.

Another new project, McHenry Row at the former Chesapeake Paperboard site on Fort Avenue, is nearly complete, with fully occupied office and retail space. Tenants include banks, restaurants and — coming in December — a Harris Teeter grocery store. Residents have begun moving into a 250-unit apartment building.

Turner said such developments and the proposed Under Armour expansion are good for the area.

Development "strengthens the neighborhood and makes it desirable for people to want to live down here," he said. "The more amenities you bring, the more people will want to live in a neighborhood."

Under Armour — which bought the Tide Point complex this summer after renting space there for years — has long anticipated the growth of its headquarters.

In 2008, the company projected that it would outgrow its headquarters in about five years. At the time, the company was considering a move to West Covington, an industrial swath of the Middle Branch that city officials had hoped to transform into a mixed-use development. But business and property owners in that area successfully fought the effort.

The latest plan has been welcomed by city and elected officials.

"Except for Domino Sugar and a few others, we don't have that much manufacturing," said City Councilman Edward L. Reisinger, whose district includes Locust Point. "For Under Armour, it's a campus and that's what they've been wanting for years. Now they're going to create jobs, they're growing, and that's good for the city. That's healthy."

Still, he acknowledges that Locust Point residents have legitimate concerns about what expansion could mean for the neighborhood.

Plank said Under Armour wants to stay put and grow, and he envisions greater recreational use of the Locust Point waterfront. Under Armour, he said, has begun talking to a neighboring company that leases storage tanks about the possibility of using that land, combined with property donated by Under Armour, to create athletic fields.

"We're extraordinarily proud to say we're adding new jobs," Plank said. "We're extraordinarily proud to say we're building new buildings. The easiest thing is to continue to expand where we are."