"Like sports, you want to watch it live," said Kevin Lin, the chief operating officer at Twitch. "You want to be there when something interesting happens. You want to be there for that moment, and share that moment as a communal experience. It's very much like being in a crowd, only digitally."
Thirty-one million Americans watched eSports last year -- up from fewer than 2 million in 2010.
It is, says Mike Sepso, co-founder of Major League Gaming, "the first sport that has gotten commercially successful outside of television."
Major League Gaming is what some call the NFL of the professional gaming world. At their brand-new arena in Columbus, Ohio, teams competed for $50,000 in prizes, as more than 100,000 watched online.
"Our typical viewer is a young guy, generally 16 to 24, maybe a little bit older," said Sepso. "He's an active gamer, who's just sort of a typical, you know, all-around American kid."
Like a lot of other all-around American kids, Matt Haag spent so much time playing video games his mother tried to stop him. "She didn't know at first, but I had extra controllers up inside the room. And I loved doing it so much, sometimes I'd be a rebel and sneak back on at night. But then she kind of wizened up over the years, and she figured out, 'Well, he's go extra controllers, I'll take the power cord!'"
Now 22, Matt is a professional gamer, known as Nadeshot. He is so good he made nearly a million dollars last year playing Call of Duty.
"I remember the first tournament that I won was this little online tournament, and we won about 50 bucks," he told Blackstone. "And I went downstairs screaming, like, 'I did it! I finally made some money!'"
He practices hours a day, as legions of devoted fans watch his training sessions online. He also has a lucrative contract with Red Bull, the energy drink company that sponsors athletes like Olympic skier Lindsey Vonn.
Does Haag consider himself an athlete? "I'd not compare myself to, like, Kobe Bryant or Calvin Johnson or anybody like that. We're not in that league. But we definitely have something that takes an equal amount of time to practice, and skill, for sure."
To hone those skills, this summer Red Bull flew Matt and his team to California for a month of real-world training.
Blackstone asked Andy Walshe, who runs Red Bulls' athlete development program, "At some point somebody came to you and said, 'We want you to start working with gamers.' Your guys work with Olympic athletes. Did you say, 'Hang on a minute here'?"
"No, I was actually the opposite -- I was really excited," replied Walshe.
Red Bull trainers put Matt and his team through the kind of intense physical workouts they do with other elite athletes: strength training, aerobics, even yoga. Red Bull hooked them up to sophisticated brain scanners to measure the stress while their playing.
When asked if he thought playing video games could be described as a sport, Walshe said, "Absolutely. You're performing at such stress loads and under such sort of stringent conditions, competitive conditions, that we call that athletics here."