jump in

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.