IDIOMS

throw one's hat in the ring

(idiomatic) To announce one's candidacy in a contest

Example: 2009, Patricia Shaw, Quadrant, November 2009, No. 461 (Volume LIII, Number 11), Quadrant Magazine Limited, page 107:
  At that time her chances had been excellent. But then two other people had thrown their hats in the ring, Joan Voller and Sidney Hamilton, and both of them were colleagues on State Executive.