noun, noun or participle which takes 'suru'
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.
彼はプールに逆飛び込みをした。
He did a headlong dive into the pool.
新しい事業
It's risky to plunge headfirst into a new business.