contrario ADJECTIVE opposite; opposing
Both the core meanings of contrario describe one thing being set against another, either physically or figuratively.
In its physical sense, you use contrario to talk about directions:
un coche que venía en sentido contrario a car which was coming in the opposite direction
Él iba en dirección contraria. He was going in the opposite direction.
In its figurative meaning you use contrario to talk about equipos and bandos contrarios — opposing teams and opposing sides:
Contini se encuentra en el bando contrario. Contini is on the opposing side.
When someone or something is contrary, against or opposed to something else, you can express this with contrario followed by a:
La resolución es contraria al espíritu del acuerdo. The resolution is contrary to the spirit of the agreement.
Martín se mostró contrario a participar. Martin was against taking part.