clench the fingers across the back part of the hand you grip.
"Around The Tea-Table"
T. De Witt Talmage
Even as she uttered the words, a terrible jar ran fiercely through the ship from stem to stern-a jar that made one clench one's teeth and hold one's jaws tight-the jar of a prow that shattered against a rock.
"Hilda Wade A Woman With Tenacity Of Purpose"
Grant Allen
He saw Glory Goldie clench her fist, and felt that she would come to their aid very soon.
"The Emperor of Portugallia"
Selma Lagerlof