Can someone please explain to me when the word "class" became an adjective? I ask because it's nearly impossible to absorb even a hour of TV/radio sports analysis without hearing someone describe someone else as a "class guy". When did this become acceptable grammar?

Follow-up questions:

1. In which sports are individuals most commonly described as "class guys"?

2. Have you ever heard said use of "class" outside of a sports-related context?

3. Who invented the "class guy"?