Watching other people play video games was once a niche pastime, but it has evolved into the massive esports market in recent years. A recent Limelight Networks survey (via eMarketer) found that American adults who play video games at least once a week spend nearly as much time online watching gaming content as they do watching traditional sports.

Chart showing weekly hours spent watching traditional sports vs. gaming videos

Data source: Limelight Networks. Chart by author.

That constitutes a big slice of the U.S. market -- the Entertainment Software Association claims that 60% of Americans play video games daily, and 72% of gamers are adults. Consulting firm Activate says that 63 million Americans watched esports league games last year, matching the number of NBA game viewers.

That's great news for Amazon's (NASDAQ:AMZN) Twitch, the country's top video game streaming platform with over 15 million unique daily visitors and 2.2 million broadcasters. YouTube also expanded into the market with YouTube Gaming, and even ESPN now regularly covers esports alongside traditional sports.

The categorization of esports as a "sport" is controversial, but the market is still growing. Newzoo expects global esports revenue to rise 27% this year to $1.1 billion, and companies invested in that market could reap big profits.