SEOUL—In a new sports ad, a brawny South Korean man stands shirtless in a pair of shorts. The camera pans six-pack abs and a chiseled jawline.

“It’s pleasurable, excitable, your heart rate quickens,” the ad’s voiceover says. “Wanna play?”

It’s not a promotion for boxing or mixed-martial arts. It’s an attempt to rebrand South Korea’s centuries-old take on sumo wrestling.

Called ssireum (pronounced “sheed-um”), Korea’s traditional wrestling has fallen on hard times. Many saw the sport as unathletic, and had little desire to watch beefy men toss each other to the ground. Once a national pastime that drew two-thirds of Korean households, TV ratings slid under 1% last year, according to the Korean Broadcasting System’s sports channel.

Ssireum’s organizers believe they have found a way to pick the sport back up off the mat: a sexy makeover.