Refers to the three loose forwards in rugby union: the flankers and the number eight. A technical sports term.
彼はバックローとして試合に出場した。
He played in the match as a back row forward.
バックローの選手はスクラムで重要な役割を果たす。
Back row players play an important role in the scrum.
Borrowed from English 'back row', referring to the back row of the scrum in rugby.