LOS ANGELES — Skateboarders have played muse for many a fashion moment. And for fall, they’re at it again. Designers here are taking elements of workout wear — sweatshirt fleece, hooded tops — and twisting them with hints of preppy or even punk. The result? Streetwise to the nth degree. Here, Paul Frank’s polyester and cotton blazer, Dogpile’s cotton graffiti blouse and Fornarina’s flared denim skirt. For more, see pages 6 and 7.