1
general::
Phrase(s): jump in((to) something)
to leap into something, such as water, a bed, a problem, etc. • She was so cold she just jumped into bed and pulled up the covers. • I jumped in and had a refreshing swim.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
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.
American Heritage Idioms