Она с ужасом смотрела на огромные кулаки Сергея. | Horrified, she stared at Sergey's enormous fists. |
Его кулаки были крепко сжаты. | His fists were tightly clenched. |
NB When the word кулак functions as a subject and does not have a descriptive modifier, the construction кулак у + Genitive is often preferred to (a) and (b), above: | |
Кулаки у него были крепко сжаты. | His fists were tightly clenched. |
левый/правый кулак | the left/right fist |
У него был сжат правый кулак. | His right fist was clenched. |