He took a few steps back the moment he realized he was about to be attacked by a bear.
He saw a bear and thought it was going to attack him, so he started walking backwards.
ーHe took a few steps back the moment he realized he was about to be attacked by a bear.
「熊に襲われそうと気がついた瞬間、彼は数歩後ずさった」
step back を使うなら、to take a few steps back「数歩後ろにさがる・後ずさる」のように言うと良いでしょう。
about to で「〜しそうである」
ーHe saw a bear and thought it was going to attack him, so he started walking backwards.
「彼は熊を目撃し、彼のことを襲ってくると思ったので、後ずさり始めた」
to attack で「襲う」
to start walking backwards で「後ずさりし始める」
ご参考まで！
He stepped back when he was about to be attacked by a bear.
He stepped back when he was about to be attacked by a bear.
He took a step back as the bear approached him.
「後ずさりする」は英語で **step back** または **take a step back** と表現します。
“step” は「一歩進む／下がる」、“back” は「後ろに」という意味なので、直訳すると「後ろに一歩下がる」、つまり「後ずさりする」という動作を自然に表します。
「彼は熊に襲われそうになり後ずさりした」は、
**He stepped back when he was about to be attacked by a bear.**
と表現できます。
カナダ 
アメリカ合衆国 
