It has been called "the biggest thing you havenít heard of." But with an estimated 250 million fans regularly watching competitive video gaming online or in person, even that description of esports is quickly becoming outdated.Tech titans and mainstream sports teams have invested millions, cable channels have shown games of League of Legends and Street Fighter, and Esports Stadium Arlington, a 100,000-square-foot arena under construction in Texas, is banking on video gamesí continued growth as a live spectator sport.On Sunday, a mass shooting at a Madden NFL tournament in Jacksonville cast the shadow of American gun violence over the nascent esports industry.Authorities have yet to suggest a motive in the shooting that killed two and injured many others. Police say 24-year-old Baltimore resident David "Bread" Katz, who turned the gun on himself and died, was the shooter. He was on an online list of gamers registered to compete that day and is known to some in the Madden community. In 2017, he fired off a last-second touchdown to win a $3,500 qualifying tournament in Buffalo, upsetting the top seed and earning praise from EA Sports for the "most exciting moment in all" of that yearís Madden series, and congratulations from the real-life Buffalo Bills.A witness told the Florida Times-Union that the shooting started after Katz was eliminated from Sundayís tournament. Court records obtained by the Associated Press show that Katz had been hospitalized twice for mental illness as a teenager and was prescribed antipsychotic and antidepressant medications.The tournament, held at a mall gaming bar connected to a pizza restaurant, attracted some of the top Madden players from across the U.S.The Jacksonville Sheriffís Office identified those killed as Taylor "spotmeplzzz" Robertson, 27, a West Virginia native and veteran Madden competitor who won the Madden Classic championship in 2017, and Elijah "Trueboy" Clayton, 22, an up-and-comer from the Los Angeles area who amassed winnings of $51,000 in his relatively short gaming career.The gaming angle has propelled the Florida attack to international news. Itís resonating not only with esports fans and players, but fans of Madden NFL. Itís one of the most successful home video game franchises of all time, with a new version released annually since 1988.Eric "Problem" Wright, a four-time Madden champion who was not in Jacksonville but is widely considered to be the gameís top competitor, wrote Monday on Twitter he was, "crying and in so much pain. Prayers to the families of Trueboy and Spotme. All over a video game. Two of our brothers are gone man and itís so disturbing."Comparing games in esports is like comparing traditional sports. Just like soccer, hockey and football donít have the same fan base, so goes competitive video games. Where games like League of Legends and Counter-Strike draw large crowds of spectators and giant prize pools of tens of millions of dollars, Madden NFL, a realistic simulation game where players control real-life NFL teams, occupies a smaller but growing niche.A core group of Madden players sit atop the rankings, competing for a smaller annual prize pool, meaning it can be harder for even professional gamers to make a living competing in Madden alone."This is usually a passion project for them more than anything else," said Roger R. Quiles, a lawyer and agent who represents dozens of professional gamers, broadcasters and esports coaches, and had a client playing in the Jacksonville tournament. "People like to compete, people like to win, but the fact is that itís a very small, very tight-knit community with Madden. Yes, emotions tend to run high, but no differently than if youíre on your couch and lose and throw a controller. Thatís generally the worst of it. So to have something like this happen is incredibly sad and something weíve never seen before in the esports world."The $5,000 tournament in Jacksonville was supposed to be the first of four qualifiers for the Madden Classic finals in Las Vegas, where the prize pool will be more than $160,000. From there, players could qualify for the Madden Bowl for even bigger money. "Weíve been concerned about safety in the industry for some time," Quiles said, noting that Sundayís tournament was open to anyone who signed up and paid the entry fee. "In small events like open qualifiers, you have pros mixing with average Joes. Thatís a great way to tie esports to its roots, but it also puts people who do this for a living at potential risk."Quiles compared the situation to a football fan showing up to a game and stepping on to the field to play alongside Tom Brady.The live tournament scene is still evolving, with tournaments varying widely in terms of security, production value and whoís allowed to compete. Itís unclear what security measures were in place at Sundayís tournament.Maddenís developer, EA Sports, has been heavily promoting this yearís competitive season. On Aug. 9, a day before the release of Madden NFL 19, EA Sports announced a partnership with the NFL and ESPN to broadcast this yearís various Madden tournaments to itís largest potential audience ever, including a tournament setup where a gamer will play as each of the leagueís 32 real-life teams.Professional gaming is a uniquely demanding sport. Competitive gamers often spend extreme hours practicing, traveling alone to tournaments can be isolating, and maintaining physical health can be challenging. Gamers who arenít signed to a team donít get paid if they donít win, and often have to supplement their income via online streaming and content creation, which also means being a public personality."Itís a lot more stressful than people think it is," Tampa resident and Street Fighter champion Du "Nuckledu" Dang told the Tampa Bay Times after winning the $230,000 prize at the Capcom Cup in 2016. "I donít really want to do this forever."Information from the Associated Press and Washington Post was used in this report.