These days it seems everyone has a podcast. But not everyone has a sterling silver Grand Slam trophy.

Whenever Andy Roddick returns to the grounds of the U.S. Open — as he did this year to record his show, “Served,” before a live audience — he no longer knows whether fans know him more for his game or his podcast.

“I have people that come up and talk to me about the show that never saw me play,” said Mr. Roddick, who is 43 but somewhat frozen in the public imagination around 21: a winsome Texas jock with spiked hair sprouting from his visor, and the last American man to reach No. 1 in tennis.

“It used to be if I walked into Starbucks and I saw a 50-year-old in tennis shoes, I knew that they would be saying something,” Mr. Roddick said in an interview. “Now it could be a 20-year-old.”

To younger people, like those elbowing him for a selfie or signature after the “Served” taping, “I’m the YouTube guy,” he said.

“Served” is now the most popular tennis podcast in the United States. It has tripled its YouTube audience in the last year to 156,000 subscribers — small by Joe Rogan standards, but significant for a niche media channel.