throw (one's) hat in(to) the ring
To announce that one is going to be competing with others, especially in a political election. I'm thinking about throwing my hat in the ring for class president! As has been widely predicted, yesterday the governor threw his hat into the ring for the presidential election next year.
throw one's hat in the ring
Also, toss one's hat in the ring. Announce one's candidacy or enter a contest, as in The governor was slow to throw his hat in the ring in the senatorial race. This term comes from boxing, where throwing a hat in the ring formerly indicated a challenge; today the idiom nearly always refers to political candidacy. [c. 1900]