Kyle Rudolph is now in his ninth season with the Minnesota Vikings, who drafted him in 2011. He has had a stable career with just that franchise, but he was involved in at least one significant trade: in his father’s fantasy football keeper league.

“My dad actually did not draft me when I came out,” Rudolph said. “One of his buddies did, and my dad traded for me, so I’m on his team to this day.”

The image of a father rooting on his son because of the fantasy implications is amusing to think about, but Rudolph’s endearing anecdote might be reasonably common nowadays.

The 29-year-old tight end is part of a generation of players who grew up as fantasy leagues were becoming part of the mainstream sports culture in the US.

No discussion of the modern NFL and its popularity is complete without acknowledging this phenomenon in which fans compete for championships of their own as owners of virtual franchises.

“I think it’s probably, as an offensive skill player, the most common thing that you hear out in public: ‘Hey, I had you on my fantasy team last year,’” Rudolph said. “Fans are all about it and it’s really changed kind of the landscape of the sports fan.”

From 2007 to 2017, the number of people playing fantasy football more than tripled, from 13.8 million to 42.7 million, according to the Fantasy Sports & Gaming Association.

On Sunday last week, ESPN’s fantasy app drew 8.3 million unique users — its biggest day ever — according to ESPN and Adobe Analytics.

Networks, Web sites and even NFL teams seem to understand the draw of fantasy leagues and their importance to fans.

“Anything that’s good for overall NFL fandom is good for the individual clubs,” Detroit Lions vice president of marketing Emily Griffin said. “We consistently hear from [fans]: ‘We want more fantasy stats, we want more out-of-town scores.’”

When Rudolph describes his father’s league, it sounds almost prehistoric compared with the Internet-powered drafts and stat trackers of today.

“They started playing in 1979 when they were seniors in high school,” he said. “Obviously at that time, you don’t have computers and Internet, you get the scores on TV afterward and get the newspaper to get the box scores, and it was points only, so it didn’t matter how many catches, how many yards, how many carries.”

Rudolph said that his dad’s league still keeps score by hand, but the Internet has obviously revolutionized the way many people follow their fantasy leagues and research players.

“There were certain things that, just, the Internet was made for,” said Rob Phythian, a cofounder of Fanball, which in 1993 began producing the magazine Fantasy Football Weekly. “The Internet was made for league management, right? It was a natural.”

Phythian identified three turning points in the growth of fantasy football.

“The first one was, I think we can take some credit for improving the content to make it more current. The second one’s league management online,” Phythian said. “The third was the leagues and the big marketing channels embracing fantasy. That came later, it didn’t come first. It came, I would say, 2003ish, where they finally gave up on saying that it’s gambling and understood it was like office pool on steroids, really.”

Now that sports betting is legal and operating in nearly a dozen states, the next innovations might blur the line a bit between that and fantasy sports.