When a player attacks without a weapon, tool equipped, or use a dedicated Fist weapon such as the Flesh rippers, they do a Fist strike. The primary attack is a punch, and the secondary attack is a kick that does additional knockback with 6x staggering. The punch has a 2-hit combo where the second punch (left hand) does double damage.
Fists can be useful against the weakest of enemies; especially when you want to avoid the cost of weapon durability. It also costs less stamina than most weapons.