f(x) popularized the tennis skirt in K-pop, especially through their 2013 comeback with “Rum Pum Pum Pum.” The group’s school-uniform-inspired styling made the pleated skirt highly visible and helped turn it into a major fashion trend in South Korea.
The look was closely associated with member Krystal Jung, whose styling during promotions inspired the informal nickname “Krystal skirt.” Clothing-industry commentary at the time credited f(x)’s appearances with a noticeable rise in tennis-skirt sales. The trend also fit f(x)’s broader reputation for experimental, fashion-forward concepts.
f(x) did not invent the tennis skirt, which had long existed in sportswear, school uniforms, and preppy fashion. The accurate claim is that they helped popularize it within modern K-pop and influenced other girl groups to adopt similar styling. Later acts, including groups using school, cheerleading, or sporty concepts, continued the look, but f(x)’s “Rum Pum Pum Pum” era is the commonly cited turning point.