Quite simply, diamondbacking is the act of not wearing underwear beneath one's clothing. Also commonly known as free balling, commando, indian, tribal, and Kramer's solution.
Invented while sweating in the summer heat of Shanghai, China.
It's too hot to be clammed up today; I'm going diamondback.
You're a fool to play hoops diamondback, Ben. You'll rupture a testicle.