The legend continues to grow for online computer game League of Legends. Immensely popular, the free-to-play fantasy combat strategy game has 32 million monthly active players, numbers matched by only the most popular Facebook games.

But other successful free games such as Candy Crush Saga and FarmVille 2 do not draw millions who simply watch others play. Last year’s League of Legends season championship final drew more than 8.2 million viewers of the live online broadcast. Top professional players can easily make six-figure incomes with winnings, sponsorships and other earnings.

This year, the League of Legends Oct. 4 final will move from the University of Southern California, where it attracted a sold-out crowd of 10,000, to the Staples Center. That an international video game championship will be waged in the same venue that has housed the NBA Finals and NHL Finals is another sign that professionally sanctioned video game competitions, also called eSports, have arrived.

“It has a lot of meaning,” says Brandon Beck, CEO and co-founder of Riot Games, the publisher of League of Legends. “I think it is going to be really exciting for fans … to see eSports being played on that big stage in front of a sold-out audience.”

Pro video game competitions and eSports have steadily grown an audience in the millions. Last year, more than 15 million online watchers saw Major League Gaming’s pro events, which featured competitions of League of Legends and other games such as Call of Duty and StarCraft II.

Last month’s MLG Spring Championship drew 21,000 over three days; millions watched the matches live online. This weekend’s EVO fighting game championship in Las Vegas is expected to attract more than 4,000 contestants — on games such as Street Fighter IV and Tekken — and thousands more spectators to the Paris Las Vegas hotel.

But League of…