defensive battle
A battle fought to defend a position, territory, or title. Used in military, sports, and competitive contexts.
They mounted a defensive battle against the enemy attack.
The champion defended the title in a title defense match.
防衛 is the general concept of defense, while 防衛戦 specifically refers to a defensive battle or match.
Compound of 防衛 (defense) + 戦 (battle, war).