public Score registerBallWinner(Player player) {
        if (player == SERVER && server == 40 && receiver < 40) {
            return new Winner(SERVER);
        }
        if (player == RECEIVER && server < 40 && receiver == 40) {
            return new Winner(RECEIVER);
        }
        Score score = calculateScore(player);
        if (score.equals(new PointScore(40, 40))) {
            return new Deuce();
        }
        return score;
    }