MEMPHIS — The fans who pack FedEx Forum for Grizzlies games never know when it will happen. It could be a timeout late in the second quarter, or a break in the action early in the fourth. It does not even occur every game.

But when it does, and the sweet beat of the Miami Sound Machine hit “Conga” fills the arena, everyone knows to look up toward the giant video board that looms over the court. A set of cartoon bongos appears, and as various fans pop up on the screen in their haphazard attempts to play them, Malenda Meacham, a longtime season-ticket holder, knows that they are merely the warm-up act.

The moment is about to belong to her.

“Bongo Lady,” the Grizzlies’ Tony Allen said, “is my home girl.”

Meacham, 45, might just be the world’s pre-eminent air-bongo impresario. She flails her arms and bobs her head as she plays the heck out of those cartoon bongos, her movements defying easy description.

“I like to think that I play enthusiastically,” she said, “and with aplomb.”

Meacham has become a minor celebrity in Memphis — people familiar with her work usually greet her by shouting something along the lines of “Hey, Bongo Lady!”

“It feels like a workout,” Meacham said. “It’s seriously like I’ve just run a marathon.”

People are generally surprised to learn that Meacham practices domestic law and works as a part-time judge. Yes, Bongo Lady is a judge.

It should be noted that Meacham has no formal musical training. Her bongo wizardry is self-taught. The key, she said, is to stay on the bongos. Too many fans let their hands drift away, which makes their playing look inexact. Meacham strives for authenticity.

“And I don’t even know when Bongo Cam is coming on,” she said, “so I can’t warm up for it.”

As is the case in most great showbiz acts, Meacham has a sidekick: her 18-year-old son, Hayden, who often accompanies her to home games. He did not choose the role. He said he was genuinely mortified by his mother’s behavior.

Hayden was with her the first time the Grizzlies broke out Bongo Cam, during the 2012-13 season. Malenda Meacham heard the music and felt the rhythm, and something compelled her to rise from her seat and start thrashing away. It was unscripted theater.

“Hayden starts going, ‘Dear God, please don’t let them see her,’ ” Meacham said. “He’s next to me, shrinking over, and then the camera catches us.”

In that moment, Bongo Lady was born. By his mother’s third appearance on Bongo Cam that season, Hayden had decided to come prepared. As soon as he heard those familiar lyrics pump through the arena’s speaker system — “Come on, shake your body, baby, do the conga / I know you can’t control yourself any longer” — he put a paper bag over his head.