go on the offensive
• take the initiative by beginning to attack or act aggressively.
• "security forces took the offensive ten days ago"
Similar:
begin to attack,
attack first,
be aggressive,
strike the first blow,
start a war/battle/quarrel,
be on the warpath,
be on the offensive
• act or be ready to act aggressively.
• "they were on the offensive from the start"