On a rooftop in Downtown LA, eight young men are preparing to fight each other for $400,000. There are hundreds of people gathered around watching, and many thousands more will tune in via an online video feed. Right now, the competitors are selecting from a range of assault rifles and submachine guns – they will need to match these carefully with smoke and frag grenades if they are to stay alive. But whatever happens, there will be a lot of death.

Fortunately, this is not a horrifying real-life take on the Hunger Games, it is the final match in the Call of Duty World Championships, a pro-gaming event pitching 32 teams against each other for a total prize pool of $1m. The venue is a gigantic tent on the top of a multistorey car park at the LA Live centre. Outside, the sun beats down on the city’s boundless concrete sprawl, but in here there is an all-enveloping artificial darkness, punctuated only by dozens of huge screens, each showing the biggest first-person shooter in the world.

Now in its third year, the Call of Duty Championship provides one of the highlights on the professional gaming – or “esports” – calendar in the US. The players taking part are the best in the world; they have qualified through a series of regional heats in their home countries, and for the last month, many of them have been practising for eight hours a day, often in houses rented with their team mates. The one thing you learn very quickly about CoD at this level is that it is a team sport – every match involves two sides, each of four players, battling through a series of punishing encounters. Victory doesn’t just go to the competitors with the quickest trigger fingers, it goes to the one’s who communicate with their comrades most effectively. Information is as vital a currency as ammunition.

All of which contrasts heavily with the cliche about this game series: that it involves little more than running around the map with a gun, blasting wildly at anything in combat fatigues. Maybe that’s true of casual players who buy the latest Call of Duty every year then flock online in their millions to compete on public servers. But it is not true here. Here, it is all about structure and strategy. It is about dedication. “Ever since we qualified it’s been non-stop playing,” says Seth “Scumpii” Abner of OpTic Gaming, one of the most popular teams in the modern scene – the Barcelona of CoD. “We actually had a LAN set up at our team house in Chicago and we flew out the team that won the US qualifiers, Strictly Business. We played for three days straight against them. It was a ton of fun, but it was work.”