jump in - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Also jump in with both feet or into the ring. Enter into something enthusiastically; also, act precipitately. For example, When Don found out what his job was to be, he was ready to jump in immediately, or As soon as they asked me to join, I jumped in with both feet, or When buying securities, Anne's apt to jump into the ring, no matter what the risks. The first two usages allude to jumping into water; the third alludes to entering the fray of the boxing ring.