逆さか飛とび込こみ

noun, noun or participle which takes 'suru'

headlong dive; header; plunge

A dive in which one enters the water headfirst, often with a running start or from a height. Can be used literally for swimming or figuratively for rushing into something.

• 彼かれはプールに逆さか飛とび込こみをした。

  He did a headlong dive into the pool.

• 新あたらしい事じ業ぎょうに逆さか飛とび込こみするのは危き険けんだ。

  It's risky to plunge headfirst into a new business.