A roar spills out of the Commerzbank-Arena, a concrete bowl that is home to German football club Eintracht Frankfurt, as dozens of young men rush through the ticket barrier, late to the match. They brush past the stewards and burst into the stadium to join the thousands of fans cheering on their idols, just as a particularly dramatic moment is replayed on an enormous screen. But there is no football, no athletic exertion and no referee here today. Instead, this contest is all about skill with a keyboard and mouse, the artful use of such weapons as the Walrus Punch, Winter’s Curse and Liquid Fire, and ruthless battles between alliances of magical heroes.

To the uninitiated, the screen in the middle of what is usually the pitch is an incomprehensible blur as the protagonists hurl fireballs at each other or obliterate marauding gangs of what look like goblins (properly known as creeps). Ensconced in cubicles at ground level are the two teams, the players sporting noise-cancelling headphones and tapping busily at their computers. In a sheltered platform off to one side, two excitable “casters”, or commentators, keep up an unbroken stream of analysis using a vocabulary that, despite nominally being English, makes you realise what English must sound like to people who don’t speak it.

Opposite them, from top to bottom of one bank of the stadium, are approximately 10,000 people, 95 per cent of them male, ranging in age from late teens to early thirties. Jeans, hoodies and team-branded shirts are the uniform but mingling with them are a few terrifying robots, a battalion of mythical creatures and more than a few scantily clad young women brandishing staffs or jagged weapons. These are the cosplayers, a distinctive tribe who dress up as fantasy characters.

Aleksandra Wysocka, a 27-year-old Polish economics and maths student, is in the blue and turquoise garb of the Crystal Maiden, a look completed with blonde pigtails and a 6ft staff with a gem at the heart of its swirling head. She and her four friends — attired as Banehallow the Lycan, Zeus, Gondar the Bounty Hunter and the Queen of Pain — drove for 13 hours from Krakow to be here today. “We go to five or six events a year,” she said. “We like this game and we like dressing up. Crystal Maiden is my favourite character. My sister is a make-up artist and helps with the masks and wigs.”

Welcome to the Dota 2 tournament at ESL One. If that does not mean very much to you, then explaining that the competition is being staged by the Electronic Sports League and the game is a variant of Defense of the Ancients will not be particularly enlightening either. To put it in the simplest terms, two teams of five are playing each other at a computer game and thousands of others, some of whom have paid more than €200 for their seats, are watching. The prize pool is $298,135.

Cosplayers attend esports events dressed as computer game, fantasy or comic book characters

Electronic sports (esports), or competitive computer gaming, is an industry on the move. Depending on who you ask, there are somewhere between 90 million to 135 million esports enthusiasts — defined as those who watch gaming regularly, online or off — and more than double that number of occasional viewers. According to a recent SuperData report, the esports sector will this year generate an estimated revenue of $621m worldwide.

Thanks in part to its big-money tournaments, Dota 2 — part of the “multiplayer online battle arena” genre, or Moba — is one of the thriving esports games. While Dota devotees are known to be particularly fervent, it is by no means the most popular title. That accolade goes to its close cousin, League of Legends. While Dota is played by around 11 million people every month, LoL has about 70 million monthly players and is wildly popular in the esports hubs of South Korea and China.

Both games are frequently described by fans and gaming journalists as having a “steep learning curve”, code for “fiendishly and bewilderingly complicated”. Dota 2, for instance, has a selection of more than 100 heroes with different capabilities based on agility, strength or intelligence. In a pregame ritual called the Picks and the Bans, which is almost as closely watched as the game itself, teams can eliminate five heroes for their opponents, which is rather like Liverpool telling Manchester United they can’t play Wayne Rooney this week. Despite their complexity, Dota and LoL dominate the viewing charts on Twitch, the most popular internet channel for esports, which was bought for $970m by Amazon in August last year.

A decade ago, South Korea was the undisputed esports capital of the world, with a particular mania for StarCraft, a military science-fiction strategy game. “StarCraft was a huge hit and helped propel competitive gaming into the public eye,” said Joost van Dreunen, chief executive of SuperData Research, a gaming industry market analysis company. But, he added, “since then the South Korean market has cooled and others, like China and the US, have emerged as leaders”.

Patrik Sättermon, the chief gaming officer of an esports team management company called Fnatic, which has offices in London and Belgrade, agreed. “Esports are becoming global, borderless,” he said. “It’s starting to look like a conventional entertainment business.”

Different games flourish in different regions. In the US, first-person shooter titles, such as Call of Duty and Halo, which are played on consoles (as opposed to a mouse and keyboard), are hugely popular. Europe takes more of a pick-and-mix approach, producing strong players across the board. While Russia, eastern Europe and Germany are all traditional esports nations, Sweden is arguably the most successful. “It is cold and dark, the people are rich and we have great broadband,” explained Sättermon.

ESL, the global tournament giant behind the packed Frankfurt spectacle, was co-founded in 2000 by Ralf Reichert. “I always wanted to fill a stadium,” says Reichert, now ESL’s chief executive. “It was always our core mission to turn this into a spectator sport, to have people competing for something — money, pride, bragging rights — and to have other people enjoying watching it.” But it took a lot longer than he had envisaged — “15 years, not the three or four we had thought”.

The cup at the event, which was won by Team Secret

Production values, as you might expect in this tech-savvy world, are as good as anywhere. In Frankfurt, prematch analysts, broadcasting live to the venue as well as over the internet, chew over head-to-head records, the statistics of star players, likely strategies and probable outcomes. “This is like the playoffs of the World Cup,” says Alan “Nahaz” Bester, a snowy-haired economics professor and esports stats guru from the US, summing up a forthcoming semi-final. “You lose, you go home.”

The players, dressed in team strips, walk to their designated cubicles amid flashing lights and huge cheers. The tournament, held over a weekend in June, reportedly had 15,000 people attending each day and online ratings of more than a million, up nearly 80 per cent on the previous year.

The eight teams demonstrate how much of an international phenomenon esports has become. The eventual winners, Team Secret, are made up of four Europeans and one Canadian, Artour “Arteezy” Babaev (all esports players are known by their nicknames: the other four Secret members were referred to as zai, s4, KuroKy and Puppey). In the final they defeated Evil Geniuses, a team that plays under the American flag but whose star performer is Syed Sumail “SumaiL” Hassan, a 16-year-old Pakistani who now lives in Illinois.

135m Estimated number of esports enthusiasts

Yet if SumaiL, a wide-eyed and painfully shy teenager who only joined the team this year, is the focus of the casters and analysts, the anchor is Clinton “Fear” Loomis. Fear, now at the ripe old age of 27, is a decade-long Dota veteran and one of its most celebrated players. When did he know esports was going places? “At TI1,” says Fear — referring to the first of Dota 2’s big-money competitions known as The International, a now annual event first held in 2011. “It had a $1.6m prize pool. That’s when I knew this would be huge.”

It was soon to get even bigger for Evil Geniuses. Last week, they won the final of TI5 in Seattle. SumaiL, Fear and co walked away with about $6.6m out of a total prize pool of $18.4m. According to the website esportsearnings.com, there are now 10 esports millionaires, all Dota 2 players.

As far as Fear is concerned, the formula to make it big in esports is straightforward. “You have got to be dedicated enough to drop school and put in the time,” he says. What about raw talent? He shrugs and grimaces. “I’m not sure how talent is really measured. The players who play more and put the effort in are the ones who make it.”

It is a sentiment echoed by Chai “Mushi” Yee Fung, captain of Fnatic (who were knocked out in the first round). A tall, diffident 24-year-old based in Malaysia’s capital Kuala Lumpur, Mushi has been playing for eight or nine years. “I practise for eight to 10 hours a day,” he said, “five or six hours as a team and then more by myself.” That is fairly standard for an elite e-sport player.

Some of the miles of cable in a behind-the-scenes tech room

Mushi leaned against a wall not far from the players’ warm-up room while behind him a young Russian woman, dressed in the skimpy outfit and long horns of a Dota hero, prepared to lead out two teams for one of the semi-finals. What makes a good team? “You have to be good players, sure, but friendship, getting on with the others, is very important,” Mushi said. “I can get cross with someone if I don’t like them.”

He confessed to having lost track of how much money he had earned over the past year, and was unsure how many tournaments he had participated in (“more than 10”). Apart from prize money, the top players have a basic salary from their team owners, a percentage of merchandise sales, sponsorship money and income from Twitch and other broadcasters for playing or practising online. Travel to the major tournaments is also paid for, as is accommodation and entertainment. And the energy drinks are unlimited — though last month a former player admitted to having gone a step further by taking Adderall, a stimulant that boosts alertness and is used to treat attention deficit hyperactivity disorder, at an ESL tournament in Poland. ESL says it will soon start random tests for performance-enhancing drugs, providing an unwelcome comparison with athletic sports.

The first competition had a $1.6m prize pool. That’s when I knew this would be huge

Completing ESL One’s pool of international talent were Chinese, Russian and Swedish teams and a couple of mixed-nationality outfits. But, even though this was a competition streamed around the world, the lingua franca was English. Commentary, analysis and interviews were all conducted in English, and in among the Germans, Scandinavians, Poles, Russians, Chinese, Malaysians and Indonesians there were thousands of British fans. The one thing missing was a top British team — there simply isn’t one.

The five players with the team Evil Geniuses at the esports tournament ESL One in Frankfurt

In a building above Fulham Broadway Tube station, a stone’s throw from Chelsea Football Club, Neville Upton, chief executive of UK company Gfinity, is trying a different strategy to build up British talent and give the consumers the shows they crave. Instead of staging a few big-money events each year, Gfinity has rented three screens from the cinema group Vue and holds weekly contests for smaller prizes, though the money on offer is hardly insignificant. At the end of June, for instance, EnVyUs and Ninjas in Pyjamas, two of the world’s top four teams for Counter Strike: Global Operations (or CS:GO — think urban warfare in a variety of devastated industrial wastelands), clashed in the final for the lion’s share of an $80,000 pot. At the other end of the scale, Gfinity stages amateur events for much smaller sums; the real lure is a chance to take on the professionals.

This, Gfinity says, is the first dedicated esports venue in the world. The set-up is similar — two teams in separate cubicles do battle on PCs while the audience watches on a big screen above them, with casters and analysts deconstructing the match. But the atmosphere is markedly different. The fans are more raucous, more partisan. CS:GO, like its console counterpart Call of Duty, enables the player to deploy an arsenal of which Arnold Schwarzenegger would approve; the best kills can be replayed in slow motion. Even so, a well-executed strategy that culminates in the bloody annihilation of the enemy draws applause and exclamations of appreciation rather than yells of bloodlust.

Syed Sumail 'SumaiL' Hassan, the teenage star of Evil Geniuses, left, and Team Alliance player Joakim 'Akke' Akterhall

“Esports prolong the life of a game and competition keeps a sport going,” said Upton in an interview shortly after the first event of Gfinity’s first season earlier this year. The company floated on Aim, the small-business section of the London Stock Exchange, in late 2014. “In the UK there are five million fanatical esports followers. But if you want to create a long-lasting impression, you want to provide weekly competition. We want to monetise this through sponsorship, advertising and broadcasting. For that, [companies and media groups] want regular events and regular exposure.”

A detail from the game involving Evil Geniuses’ SumaiL

It is a bold move, and one that may yet spur a group of British youths to abandon their A-levels and take a professional approach towards esports. ESL is also setting up its own UK leagues, hoping this will produce homegrown winners who can go on to the top global events. “Instead of flying in elite players, we are trying to build up the quality of British teams from small, grassroots competitions,” said James Dean, who represents ESL in the UK. “If we can then bring the best to the global scene, we hope the fans will stick with us.”

So far, however, British teams are firmly in the second tier. “The UK is a financial powerhouse with a big and wealthy market,” said Fnatic’s Sättermon. “But maybe you think this is all still a bit geeky. In Sweden, we have moved out of the basement and into the big arenas.”

Even though the internet is where most gaming takes place, it is the live tournaments that have the real prestige, events where the best of the best compete on equal terms, with the same broadband speeds and the same computers. These are the apex of a phenomenon known as the LAN party, short for local area network, which has existed almost since multiplayer games were invented. One of the most celebrated LAN events is DreamHack, which started life in 1994 in a school canteen in Sweden. It has grown into a festival comprising gaming, competitions, digital art, live music and exhibitions of the newest gear and game releases, with offshoots all over Europe. DreamHack has a competitive element but is also a broader celebration of gaming culture, with fans participating in bring-your-own-computer contests and queueing to meet esports celebrities.

Cosplayer Maximilian McKone watches the games action on a big screen

The big question for ESL and its competitors is how to maximise revenue in the way that traditional sports have. “The esports enthusiast is extremely valuable for big brands, digital media providers and hardware manufacturers alike,” said the esports market research group Newzoo in a 2015 report. “Participants and viewers are more likely than the total population to have a Netflix or Spotify subscription, to have a high income, a full-time job and a big budget for the latest hardware devices.” Indeed, the industry as a whole — games, consoles, gaming PCs, headsets, in-game upgrades, joysticks and racing wheels — is worth around $100bn a year. The challenge for esports is to build revenue from broadcasting, advertising and merchandise when the fans and players may be content with things as they are.

Sean Charles, ESL’s vice-president of partnerships and publisher relations, is optimistic about the industry’s development. “The analogy I use is motor sports,” he said. “In the early years, you only saw the same brands attached to the individual teams but, as the viewership grew and you got the wow factor, advertisers realised they could reach a large volume of people. That ‘spring’ moment is a very tell-tale moment for any form of entertainment, and that is where esports is now.” Ten days after we spoke, the Swedish media company Modern Times Group, which operates free-TV and subscription satellite channels in 100 countries, bought a 74 per cent stake in ESL’s parent company, Turtle Entertainment, for $87m.

Esports opens up a clear generational divide. At every tournament, it is truly disconcerting just how young everyone is — not just the players but also the fans, technicians, cameramen, team managers, PR officials, journalists from specialist trade publications, casters and analysts. But for anyone who regards an obsession with computer games as a fast track to the moral and physical degeneration of the planet’s youngsters, it is equally striking how so many of these people are clean-cut, friendly and wholesome. Instead of flinging obscenities at the teams or each other, rival fans applaud exciting and successful manoeuvres by both sides. Rather than mocking the cosplayers as a football crowd might do, everyone wants to be photographed with them. In the often fevered environment of a football stadium, such a decorous atmosphere is almost unnerving.

$621m Estimated revenue the esports sector will generate this year

Rasyid Naif Dahbul is a 22-year-old Indonesian with an enormous mouse mat draped over one shoulder as he queues for autographs from the members of Team Alliance. The queue is about 50 metres long and Dahbul is near the back but he is undaunted. His mouse mat is already well covered with the names of any and every player he has managed to meet. A web developer from Jakarta, Dahbul is doing an internship with a Berlin-based company. He is a long-time Dota 2 fan and is clearly delighted to be in the same country as one of the game’s leading tournaments.

“The premium ticket [costing more than €200] was expensive but otherwise the cost of travel and accommodation was not bad,” added Dahbul, who booked through Airbnb. A premium ticket entitles the holder to the best seats, free drinks and food for the weekend — great as long as you like large amounts of Brätwurst and lasagne — a goodie bag and access to signing sessions.

Dahbul’s friends are mostly wearing the striking canary yellow of Natus Vincere, better known as NaVi (for some reason, esports teams have a fondness for Latin names, such as Vici, Invictus and Dignitas). Because NaVi did not make it through to ESL One, Dahbul has recently switched allegiances to Evil Geniuses. “I like to be on the winning side,” he chuckles.

Line-ups for the two finalists, Evil Geniuses and Team Secret

Signing autographs at the end of the queue is Alliance star Joakim “Akke” Akterhall, 27. Akke has Swedish good looks, immaculate hair and a sharp-edged black jacket with an array of Velcro panels so that sponsors’ logos can be stuck on and peeled off as the occasion demands. He has nearly 70,000 Twitter followers, a degree in computer science and, according to esportsearnings.com, has earned $418,300 from 72 tournaments, much of it from winning The International in 2013.

Akke began playing Dota with his school friend and teammate Jonathan “Loda” Berg when the game was still new. “We realised we were quite good and so we started to play tournaments until we won a big one online,” he said. The other members of what became Team Alliance were recruited on the internet. “It’s like any other work group. They have to understand how you want to play, you have to fit well as a team. You want it to be fun but you all have to have the mindset to win.”

Commentator Austin 'Capitalist' Walsh used to be a reservist in the Marines before becoming a 'caster'

Shortly before the climax of ESL One, I am led out into the middle of the stadium, between the fans and the teams, by Austin “Capitalist” Walsh. The Capitalist, a 24-year-old American, is due to commentate on the final with famous caster Toby “TobiWan” Dawson. Before that, he guides me through the basics of Dota 2 as Evil Geniuses win their semi-final with ease. He attempts to explain such alien concepts as ganking, the laning phase and mana points.

“Regular sports commentators have been working for decades — they are more experienced and more technically proficient,” said the Capitalist. “But the rules of esports are more complex and can change from one year to the next — new heroes, new maps [playing territories]. A sports commentator who retired a decade ago could come back today and do a reasonable job. An esports caster who quit two years ago could not possibly cast a game now.”

The Capitalist had been a reservist in the US Marines for five years when, after gaining some experience as a caster, he was offered a job with German esports marketing agency Freaks4U Gaming, which runs one of the big Dota 2 community websites. “I remember having to tell my gunnery sergeant why I was going off to Berlin,” he laughs. “He accused me of going to work for a German porn site.”

We turn away from the game and look up at the crowd. With the tournament approaching its final stages and the spotlights flaring in the gathering gloom, the excitement and tension are beginning to intensify and the seats are filling up. On the platform before the screen stands the ESL One trophy, waiting to be claimed. When the players emerge into the stadium, this is what they will see.

The Capitalist, trim and besuited, looks up and grins. “It’s quite something, isn’t it?”

Barney Thompson is a reporter and editor on the FT’s UK news desk

Photographs: Sabine Reitmaier