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1.
To throw one's hat in (as "in the ring") is to:
1) to challenge or contend for something.

2) nominate someone or oneself for something. To volunteer.

A boxing metaphor that originated in the early 19th century when one who wished to challenge a boxer would throw his hat into the ring as a way of having your challenge noticed in a crowded ring.
In 1912 Theodore Roosevelt, who was an advid boxer, was the first presidential candidate to use "throw my hat in the ring" to announce his run at the U.S. presidency.
by Tenacious Faulker April 04, 2009