Counterattack
Counter Offensive
noun, する verb
Anti aggression is when you receive some aggression, then respond to it with anti aggression, aka your counterattack.
はんこう
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
いつ誰に対して織田軍が反攻を開始したのか覚えてる？
Do you remember when and who Oda’s army started the counterattack against?