head-first BrE AmE , head‧first /ˌhedˈfɜːst◂ $ -ˈfɜːrst◂/ adverb
1 . if you fall head-first, your head goes down first, and the rest of your body follows afterwards
dive/fall/jump/plunge head-first
I fell head-first down the stairs.
2 . if you do something head-first, you become involved in it too quickly, without having time to think about it carefully:
a remark that sent him tumbling head-first into another controversy