There is a Legacy version here.

Unarmed

Source Player Core pg. 283 2.0
An unarmed attack uses your body rather than a manufactured weapon. An unarmed attack isn’t a weapon, though has a weapon group and might have weapon traits. An unarmed attack can’t be Disarmed. It also doesn’t take up a hand, though a fist or other grasping appendage generally works like a free-hand weapon.