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Used to refer a professional athlete. This athlete is of such superb skill, and athleticism that place them at the top elite of their class in the sport they play. Diamond class is a very small group and, only the best of the best are referred to in this way.
Man: "Wow look at #81! He just made a play that was impossible.. and made it look easy."

Friend: "He is definitely Diamond Class!"
by Bageez March 11, 2014