a person's hand when the fingers are bent in towards the palm and held there tightly, typically in order to strike a blow or grasp something

she pummelled him furiously with her fists

Karr clenched his fists

strike with the fist

he fisted a goal-bound shot over the bar

clench (the hand or fingers) into a fist

she fisted her hands on her hips

penetrate (a sexual partner's anus or vagina) with one's fist