Feline Longmore hadn’t anticipated having fans. She didn’t grow up playing the game in which she is now nationally ranked. She doesn’t look much like the average competitor, either: Far from the stereotypical teenage boy gamer, Longmore is a 31-year-old woman.

And yet, here in the starkly lit, heavily air-conditioned ballroom of the Walter E. Washington Convention Center on Sunday morning, she has fans. Lots of them. Toward the end of each round of the Star City Games Open Series tournament — the country’s biggest competition for the fantasy card game Magic: The Gathering — crowds of admirers tend to gather around Longmore’s table. One bespectacled teenager hovers nearby during every round. He’s the proud owner of a Longmore-autographed High Tide — the card she is famous for playing — obtained at a different tournament. But he doesn’t say anything about it. He just watches.

The response to Longmore’s success hasn’t always been so positive. When she won a similar tournament in Seattle two years ago, the online backlash was virulent. The day after her victory, a thread went up on a message board for gamers titled “Magic The Gathering Legacy tournament champion is a chick. Would you hit it?” When commenters found out that Longmore is transgender, their language became even more venomous.

This was the Magic world asserting its boundaries. Invented in 1993 as a quick trading-card game that could be played between rounds of Dungeons & Dragons, it’s a fairly geeky pastime even by gaming standards. Some players have said they got involved in Magic in high school because they weren’t cool enough to hang out with the kids who played video games. For them, Magic was a refuge, the one clubhouse where they could be themselves.

For nearly two decades, that clubhouse has included mostly young, white men — a demographic that still makes up about 90 percent of tournament participants.

But Longmore’s success, and the recent success of other female players, set off something of a crash course in diversity training for Magic players. It had to. The game isn’t just some extra-obscure corner of the offbeat nerd community anymore: It’s a $200 million-a-year industry with a fan base of 20 million and a growing pool of elite players who make their living from tournament prizes (which top out at about $40,000). There’s even a Magic movie in the works.

“That kind of behavior, it’s just not healthy for the game,” Cedric Phillips says of the online vitriol directed at Longmore and other female players. A former professional player-turned-play-by-play announcer for Star City Games, which organizes tournaments, Phillips watches the Magic community more closely than almost anyone. And he does see it improving.

He attributes the change, in part, to demographic shifts that are happening across the gaming culture. According to a report released by the Entertainment Software Association in the spring, women make up 48 percent of all computer and video game players, and the average age of gamers is 31. Similar data for tabletop games such as Magic is hard to come by — but John Ward, executive director of the Game Manufacturers Association, says that, anecdotally, he’s seen more women become involved in these kinds of games as well.

Gaming is becoming more mainstream, Phillips says, and as it does, it’s growing more diverse. Magic offers a case study for the question all games will soon face (if they aren’t already): As the community expands, can it drop its no-rules, boys’ club mentality?

“Gaming has always been perceived as a guy thing to do,” says Tifa Robles, founder of a Seattle-based group that aims to cultivate a more welcoming Magic community at local game shops. “So either someone was hitting on you, or they assumed that women don’t know what’s on their cards the same as men do.”

Andy Bruce, a competitive player who participates in three to four tournaments a week, has written extensively about what it’s like to be a woman in Magic: people staring at her chest, speculating about her underwear, asking her if she was going to take her shirt off so she could win.

Bruce found similar testimonies from other female players online and realized the breadth of the problem. It goes beyond Magic, too. Bruce pointed to Anita Sarkeesian, whose video series “Feminist Frequency” draws daily threats and crude remarks for its critiques of how women are portrayed in video games.

It’s difficult for gamers to pinpoint the source of these attitudes: Is it the immaturity of players? A belief that women don’t belong in the gaming world? But they do see something of an explanation in gaming’s origins. So many people come to gaming because they were excluded elsewhere — and they can be irrationally defensive of their communities once they’ve found them.

“When you have that level of ostracism and feeling like you’ve made a clubhouse, anything that threatens the way you look at it is really, really dangerous,” says Elizabeth Sampat, a game designer and steering committee member of the International Game Developers Association’s “Women in Games” special-interest group. “This is their territory and they have to defend it, no matter what.”

It is slowly, by some measures, getting better.

Robles, who took time away from competing when she was working for Wizards of the Coast, is again playing and no longer the only woman at tournaments — female players typically now make up 5 to 10 percent of tournament participants.

And behavior at competitive events is being more tightly regulated. In conjunction with Wizards of the Coast, the network of volunteer judges who run tournaments instituted new rules this summer that broaden the definition of “unsporting conduct” and allow judges to bar players for offensive language and harassment.

Helene Bergeot, Wizards of the Coast’s director of global organized play, didn’t comment on whether there was a specific reason for the rule change. But she did say that the company recognizes Magic’s widening fan base, “and that’s also the reason why we are striving to make the Magic tournaments as welcoming as possible.”

Longmore prefers to stay out of those politics. Unwilling to let anything get in the way of her game, she hasn’t paid attention to the backlash from her 2012 victory in Seattle or any that have followed.

Even at Sunday’s tournament, which isn’t going as well as she’d hoped, she stays upbeat. Though it’s clear by the fifth round that she is not going to make the top eight — her original goal for the day — she decides to stay through the afternoon. She loves the game, and because she’s gunning for an invite to the Players’ Championship at the end of the year, it’s good to play as many matches as possible.

A friend checks her next assignment for her, and Longmore walks over to a table where a young man is already shuffling his deck. He looks at her as she sits down, then at the cards in her hand.

They shake hands, and when they begin to chat, the man’s first question isn’t about Longmore’s gender. He wants to know about High Tide, the card she’s famous for playing.

Longmore smiles and dives in.

CORRECTION: An earlier version of this story incorrectly stated that Hasbro lists “Magic: The Gathering” as a “boys’ action gaming product. The company lists Magic in its “games” category. This version has been corrected.