Former NBA player Rick Fox is on the phone when he receives another call: It's from Denmark.

"I have to take this," Fox says.

When the three-time NBA champion clicks over, the voice on the other line is of a young, Danish man who is being wooed by a host of North American esports owners. Fox, who purchased an esports franchise in December for an undisclosed sum, is one of those owners. Fox wants the gamer so badly that he's not willing to give up his name for fear it will make it harder to land him. And Fox certainly won't talk about how much he's willing to pay.

"Everything that is happening in esports is starting to mirror the rise of pro sports," said Fox, who expects his Echo Fox franchise to have teams in all the major disciplines, starting with Dota 2, Heroes of the Storm and Call of Duty.

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From humble beginnings, the appetite for esports has skyrocketed as its acceptance has spread from Asia to Europe and now to the United States. In October, tickets to the the League of Legends World Championship Final at Berlin's Mercedes-Benz Arena sold out in three minutes. In the U.S., the LoL World Championships sold out Staples Center in Los Angeles in less than an hour in 2013, and the Dota 2 International sold out Key Arena in Seattle the last two years. For those watching online, the final between SKT and Koo Tigers saw a peak of 14 million people tuned in at the same time, according to Riot Games, the creator of LoL.

The business of watching gamers play has grown so fast that up to 200 players are making at least $40,000 in prize winnings as professional gamers, according to Tobias Sherman, who heads up WME/IMG's esports operation. And that number is growing. To put the $40,000 in perspective, it's about what the 150th-ranked men's tennis player and 330th-ranked golfer in the world gross a year.

"Every team has coaches, managers, analysts, psychologists and even more. Players don't have to care about anything anymore besides the game." Marcel "Dexter" Feldkamp, League of Legends pro

Information on players' salaries is harder to find, but Valve, the manufacturer of Dota 2 and host of its top tournaments, lists the top earner in 2015 as Peter "ppd" Dager, who made more than $2 million in prize money. One player, Saahlil "UNiVeRsE" Arora, took home more than $1.3 million in the single biggest payout of the year from the Dota 2 International. That's out of a total esports prize money pool of $64 million in 2015, according to Valve.

Fox has been studying the space for several years, turned on to it after years spent playing games with his now 21-year-old son, Kyle. Fox says after three years of investment and education in esports, he finds that parents, who used to do the talking for their talented gamer son or daughter, have now often been joined by an agent or a lawyer. Fox himself is equipped with a director of scouting.

Offers for the top guys, many of whom are in South Korea and China, include not only financial incentives but also free education in the future. Fox, for example, will have a college fund in their contracts.

"It used to be that there was no value in dropping out of school to start a video-game career since [a career competing in video games] didn't exist," Fox said. "Now a kid can go to mom and dad and say, 'Look, I have an offer with real money.'"

And as the stakes rise, so too do the amount of professional services that are provided to the gamers.

"Every team has coaches, managers, analysts, psychologists and even more," said Marcel "Dexter" Feldkamp, a League of Legends pro from Germany who plays for a team called Legends. "Players don't have to care about anything anymore besides the game."

Fox is just one of several in a new age of investors who have identified the opportunity.

Amazon bought gaming channel Twitch for nearly $1 billion in August 2014. WME/IMG brought an esports league concept to Turner Broadcasting, which will air 20 live events on TBS this year with a total prize purse of $2.4 million. Former NBA commissioner David Stern was a small investor in esports fantasy company AlphaDraft, which was sold to FanDuel in September. ESPN has been broadcasting esports online for years on its ESPN3 platform, but the shift to mainstream TV came in April of last year, when ESPN2 aired "Heroes of the Dorm," a Heroes of the Storm competition among college teams.

And there were two head-turners in the first week of the new year, with Activision buying Major League Gaming, which streams live competitions on its website, for $46 million in cash, as well as Mark Cuban buying a piece of esports analytics firm Fantasy Labs for an undisclosed sum. Cuban had already put his money into esports wagering platform Unikrn.

Mark Cuban plays in a charity League of Legends match against Intel CEO Brian Krzanich last November. Cuban is an investor in an offshore esports gambling company called Unikrn, and Intel has been a sponsor of esports for over a decade. Carlton Beener/ESL

Tobias Sherman was a third-generation golf course owner who grew his business by finding a way to simplify online tee times for boomers. Having built a nice side career as a poker player and growing tired of the family business, Sherman, at 31, told his wife he was going to take a year off.

This was in 2010. Around the same time, Sherman's older stepbrother, Dale, was bothering him about looking into the growth of esports. Dale is 12 years older, but the common thread between the two brothers was playing video games together.

Sherman had been playing StarCraft, Broodwar and Counter-Strike, the games that just happened to evolve into the original esports platforms. But at the time, he didn't believe it when Dale told him that there was a group of people who were willing to watch others play.

Sherman put it off for a while, but when he eventually gave in and watched footage of gamers playing in front of 40,000 fans packed in a South Korean World Cup stadium, he became convinced.

"It was amazing," he said. "Just like watching a sporting event, but actually better."

Sherman's way into the business was as an announcer. He called Simon Abitbol, who ran the largest amateur Starcraft tournaments, and offered his services to call the action. Abitbol agreed, and during the time Sherman was behind the mic, entries grew from 50 a night to more than 1,000. That's when he got a call from Major League Gaming to do the same thing for them.

"It was a great way to meet and interact with the talent and players and develop their trust," Sherman said.

Once he became a familiar name, he moved on to his strategy of representing them, which was easy to do given that the business was still in its infancy.

Sherman grew Global eSports Management into a boutique agency that represented teams and players with offices in Miami, Berlin and Seoul. In 2015, his business was acquired by IMG for an undisclosed sum.

Sherman is excited about the upward trajectory of the business, which some analysts say could be worth $1 billion by 2017. That's a huge jump from the $130 million business esports was said to be in 2012, according to market-tracking analyst NewZoo.

But he's also scared.

"There's a lot of gunfights going on right now between teams, game creators and leagues," Sherman said. "There's no draft system, there are poaching owners torturously interfering with players who are already under contract with teams."

As esports has grown and the money has risen, Sherman said, "Greed is what will kill this industry, and right now, it's the Wild West."

For his part, Cuban thinks another challenge facing the industry is the age of esports pros and the relatively short period of time they can compete at the highest level. Also, game manufacturers modify their games through patches sometimes several times per year. Changing how a game plays has forced some pros into retirement because they can't adjust.

"How to manage a team of players is the biggest similarity right now [to traditional sports]," Cuban said. "But also the biggest challenge. Sixteen-year-old kids are tough to manage. The fact that games often change their 'rules' monthly, necessitating players practicing 10 or more hours a day, also makes it very different. As does the fact that veteran players often burn out and retire before they are 21."

The International Dota 2 Championships, held last August at Key Arena in Seattle, was the richest purse in esports history at $18.4 million total. North American team Evil Geniuses split the first-place prize of $6.6 million. Courtesy of Valve

Over the past couple of years, Feldkamp has had a front-row seat to the growth of esports, not only through play but as a commentator. As money came into the sport, Feldkamp saw the rise of professional support services that are similar to regular pro sports.

"Some can thrive in that [competitive] environment a lot better than others," Feldkamp said. "Competition gets tougher every year, though, simply because of the huge popularity and the increase in player base."

With more competition, there are more people trying to find an edge. Controversy occurred last March when a former Cloud9 player said his team had taken Adderall to keep them more wired during competition. The promise of random drug testing has followed, but it's not yet clear how comprehensive it will be across the esports landscape with no official governing body yet to standardize the sport.

Coca-Cola is one of the most well-known brands in the world, and obviously doesn't make games or accessories. But, after sponsoring League of Legends tournaments for a few years, Coca-Cola now produces a weekly online show about esports. It's following the lead of two other brands that have spent a decade cultivating relationships in esports: Intel and Red Bull.

Intel's participation began with its sponsorship of worldwide esports tournaments in 2006 called the Intel Extreme Masters. "[League of Legends] has got the same complexity and strategy and teamwork that basketball and football and any other of the traditional sports have," said Intel CEO Brian Krzanich, who has been at Intel since 1982. "I found people are dedicated and they practice as many hours as a professional basketball player does and they're just as focused and driven. ... It's one of the fastest-growing spectator sports around the world. It's truly worldwide."

In 2006, esports landed on the radar of Red Bull executives. Instead of just sponsoring athletes, the world's best-selling energy drink has a media arm that produces around-the-clock content with their athletes.

After running and filming tournaments for three years, Red Bull took it a step further by building an esports broadcast studio in Santa Monica, California, where their sponsored players and teams can also train.

"I found people are dedicated and they practice as many hours as a professional basketball player does and they're just as focused and driven. ... It's one of the fastest-growing spectator sports around the world. It's truly worldwide." Brian Krzanich, Intel CEO

"We configured a gaming desk, we have all the wiring a gamer needs, we can even monitor eye movement," said Lukas Cudrigh, head of digital for Red Bull Media House in North America.

Red Bull has a roster of players including Matt "Nadeshot" Haag, who at one time was the world's top Call of Duty player and is one of the industry's most well-known streamers. Haag's team, OpTic, first won $400,000 at a Call of Duty tournament in 2011 and was the first esports team to win an X Games gold medal. OpTic Gaming will be the first esports team with a book deal, signing a contract with HarperCollins reportedly in the high six figures with an anthology due out this spring.

Red Bull has also recently announced sponsorships with a couple of teams, including Cloud9's League of Legends team, which promised to start training out of Red Bull's facility.

Cudrigh wouldn't say how much the company is spending on the efforts, other than to say it's obviously significant.

Meanwhile, Fox is just starting out, but he admits he's as obsessed with making his dreams come true as an esports team owner as he was in his quest to become an NBA player.

"I want to build the pre-eminent esports empire," said Fox, whose team will first compete under his ownership in the League of Legends tournament this week.

In late December, Fox was at a convenience store when a group of people walked up to him. They weren't North Carolina basketball or Lakers fans.

They wanted to congratulate him on buying an esports team.

Additional reporting by ESPN writer Arash Markazi.