adversarial
ad·ver·sar·i·al
/ˌædvɚˈserijəl/ adj [more ~; most ~]
formal : involving two people or two sides who oppose each other
The two men have always had an adversarial relationship. [=they have always opposed each other; they have always treated each other as adversaries]
an adversarial system of justice with prosecution and defense opposing each other
