clench

He began to clench his fists in anger when he heard the unfair accusations.

(Chinese) 当他听到不公平的指责时，他愤怒地攥紧了拳头。

The patient had to clench her teeth to endure the sudden sharp pain in her leg.

(Chinese) 病人不得不咬紧牙关以忍受腿部突然产生的剧痛。