def opponent_rank(self):
        """
        Returns a ``string`` of the opponent's rank when the game was played
        and None if the team was unranked.
        """
        rank = re.findall(r'\d+', self._opponent_name)
        if len(rank) > 0:
            return int(rank[0])
        return None
Returns a ``string`` of the opponent's rank when the game was played
        and None if the team was unranked.