"It's a legitimate sport, and there are millions of fans around the world who pay good money to watch you play," says professional League of Legends player Yiliang "Peter" Peng. "There are a bunch of sponsors around the world who pay thousands and thousands of dollars every month just to put their name on your jersey."

With nearly a billion hours of logged game play and over 70 million unique accounts, League of Legends has become the fastest-growing game in the world.

Born through open-source tinkering of a game named Defense of the Ancients, League of Legends is a free online multi-player battle arena powered by a community of 40 million regular players. While the game's concept is not unique—its strategy is similar to that of chess—the platform has enjoyed a meteoric rise to the top of the video game industry since its release in October 2009.

Though many video games have amassed cult-like followings over the years, League of Legends stands out because of the emphasis placed on its professional players. Riot Games, the developer behind League of Legends, used its players' feedback to make improvements and added production values by showcasing battles as a spectator sport.

"League of Legends…has done so well because first they built a game that was really, really fun," says Steve Arhancet, director of eSports at Curse Gaming. "Then they listened to their community."

While some may scoff at the notion of video gamers as professional athletes, Riot Games has spared no expense in emulating the look and feel of a pro sports event. Every live League of Legends competition comes complete with a Jumbotron, professional announcers (called "shoutcasters"), concessions, and die-hard fans. The live events are so popular that in its third season, League of Legends sold out the Staples Center in Los Angeles for its world championship. Events in Shanghai have drawn crowds in the hundreds of thousands. While it's still unclear whether the success of League of Legends is a fluke or a trend, many gaming experts predict that this is just the beginning of the emergence of eSports into popular culture.

You can download League of Legends for free here.

Approximately 5:30 minutes.

Produced by Will Neff and Scott Shackford. Camera by Alexander Manning.

Music by: EnV—Bonus Level