At the beginning of a match, hold the Left Analog-stick Up/Right to start out with possession of the Quaffle, making it easier for the first score. Usually making the first score assures that you will win the match as long as you follow the other scoring tips. When hitting a Bludger, make the Bludger go directly in front of the other team's Chaser that has the Quaffle. Then move the Analog-stick Down and in a few seconds the Bludger will hit the Chaser; and you will have possession of the Quaffle.
