expression, godan verb (-ru)
start a fight; open hostilities; kick off a conflict
Idiomatic expression literally meaning 'to cut the matchlock cover', referring to the action of opening the pan cover on a matchlock gun to fire. Used figuratively for beginning a battle, argument, or confrontation.
両チームの応援団が火蓋を切った。
The supporters of both teams started a confrontation.
彼の一言が議論の火蓋を切った。
His single remark sparked the argument.