四分律刪繁補闕行事鈔 2.314

2.314

掉臂者，垂臂前却也。不犯者：病、為人打、及餘緣舉手遮、浮渡水若以手招喚伴者。

Swinging the arms means hanging the arms down and swinging them forward and back. One does not commit an offense if: ill, beaten by someone, or raising a hand to ward off other perils, swimming across water, or gesturing with the hand to summon companions.