Ryuko does not wear a regular Stadium jacket. What she is wearing is a Sukajan (スカジャン) Jacket.
Sukajan jackets were once worn by juvenile delinquents, yakuza, and rebellious youth. That association still exists today but to a lesser degree than in the past.
These are often made of shiny material with intricate embroidery on the front and back. In Sushio’s early sketch for Ryuko, she was supposed to have a dragon embroidered on the back of her jacket, which is a popular design for Sukajan. The Ryuko Cospa Jacket which was worn by Sushio and Ami Koshimizu is also made of a shiny material similar to a Sukajan jacket.