Threw one's hat in the ring (3)
I believe the answer is:
ran
'threw one's hat in the ring' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for ran that I've seen before include "Took to one's heels" , "Organised" , "Administered" , "Tore" , "Operated; hurried" .)