On most days, they are fierce competitors in an intense battle for virtual dominance. But after the shooting at a Madden NFL 19 tournament on Sunday, professional video gamers were united in shock and grief.

Pro gamers tweeted tributes and condolences to the two players who were killed, revealing the bonds forged in the shopping malls, sports bars and movie theaters where they typically go head-to-head over keyboards and mouses.

"One of the most tragic days I've experienced," Eric "Problem" Wright, a top-tier player of Madden, posted on Twitter. The megahit football game franchise had brought enthusiasts to the tournament in Jacksonville, Florida.

"This community is like family. Broken," Wright added in his tweet.

Tony Montagnino, a gamer who was wounded in the shooting, suggested in a tweet that he was heartened by what he saw in the wake of the bloodshed — "a community of people rally around each other."

Just wanna say RIP to my madden brothers @True__818 and @spotmeplzzz you guys didnt deserve this. Your families didnt deserve this. Gone way too soon. — Trey God (@Draggg_) August 26, 2018

The violence inside the GLHF Game Bar, a venue that bills itself as a "home for gamers and nerds alike," draws attention to the world of competitive video gaming, or esports, a fast-growing cultural phenomenon that also includes titles like "NBA 2K," "Pokémon" and "Call of Duty."

What was once an under-the-radar subculture has become a multi-million dollar behemoth in which players style themselves as traditional athletes, vie for sponsorships and duke it out — trash talk included — for large cash prizes.

You can watch countless hours of the action on Twitch.tv, an online network where gamers live-stream their digital exploits for all the world to see. The network attracts tens of millions of viewers.

"Twenty years ago, the stereotype was that gamers were outcasts who lived in their parents' basement. But that image has changed dramatically," said Joost van Dreunen, an adjunct assistant professor at New York University who teaches a course on the business of video games.

"Everyone plays Candy Crush," he added, referring to the popular puzzle-themed mobile app. "Everyone's a gamer. What we're looking at is the transition of a form of entertainment from the fringes to the mainstream."

This year, the worldwide audience for esports is on track to reach some 380 million people — and the overall market is expected to hit $905 million, according to the research firm Newzoo. Esports could even be featured as a sport at the 2024 Olympics Games, according to reports.

Video gaming tournaments have become major attractions — and the stakes are getting higher. The prize pool for last year's annual event for fans of the fantasy game "Dota 2" climbed to more than $20 million. (The contest in Jacksonville came with a comparatively modest $5,000 prize.)

Eduardo Deno, 21, of New Jersey, who is seen as a rising star among players of a game based on the Japanese anime series Dragon BallZ, has said he aspires to buy a home for his family with his winnings.

"I would tell my mom, 'Oh, you didn't believe video games [were] this popular, I could make money off of it?'" Deno said in a recent Sony Crackle web documentary. "'Well, you see this house?'"

Madden NFL, named for John Madden, the Hall of Fame coach and former TV commentator, is particularly popular, bridging generational divides with each annual installment. As of late 2013, the series had generated more than $4 billion revenue for its publisher, Electronic Arts, or EA.

The series, which debuted in 1988, also boasts a loyal following of players who spend countless hours mastering the game and refining techniques. The flagship Facebook page for the series has more than 4.7 million likes, and more than 46,000 people subscribe to the /r/Madden forum on Reddit.

In a statement posted on Twitter on Monday, after the two slain gamers were identified by officials as Elijah "TruBoy" Clayton and Taylor "SpotMePlzz" Robertson, EA said: "Many of us at EA knew Elijah and Taylor well, and their positive, competitive spirit and respect for other players was evident to everyone."

The tournament circuit, by many accounts, breeds rivalries. But it also fosters conviviality among players.

"Guys work together, it’s like the NBA and NFL. We're athletes that are also a family," said Jesse "Champ2k" Buddle, a former Madden gamer who said he knows some of the victims and now plays NBA 2K, which had its inaugural season this year. "Not everyone likes each other, and not everyone gets along, but we’re competitive and we're close — a family."

Buddle said that at recent events he has seen better protection, and even metal detectors, but "this wasn’t a larger Madden event, so maybe that's why there wasn't a lot of security there."

The man police identified as the shooter, David Katz, 24, who took his own life after opening fire, had achieved some prominence on the Madden circuit.

Katz was listed online as a 2017 championship winner — a victory that EA said at the time had been called "the most exciting moment" of the competition, according to a cached version of the company's website.

Authorities have so far declined to discuss a possible motive for the shooting. In the absence of answers, some professional gamers appear to be left with conflicted feelings about the hobby that has effectively become their careers and livelihoods.

"Crying and in so much pain," Wright, the Madden player, said in a tweet. "All over a videogame."

CORRECTION (Aug. 28, 2018, 9:08 a.m.): An earlier version of this article misstated the first name of one professional gamer. He is Jesse Buddle, not Eddie.