This is a simple classic that's been used by everyone from Tupac to Big Boi to Mos Def. It's a versatile move, perfect for park bench freestyles (see movie below) and battles.
The arm is lowered but bent at the elbow so that the hand is shoulder-height. Your fingers should be extended and pressed together almost like a Miss America wave. Now angle your arm down a little so you don’t look too much like Miss America and shake at the elbow. Works well with a corresponding head shake.
The best emcees add varation by throwing in other moves or by angling their hand farther down. You can flip this one horizontal, almost like you’re scratching a record. It’s all about the rhythm.