The main objective of the defending team is to recover the ball to prevent the opposition team from scoring. This is done by using the Movement Dice (the black one) and the Challenge Dice (the blue one).
Let's say the white team advances its attack, but now is the turn of the blue team, which will try to recover the ball:
When a defending player stands in front of the player who has the ball, a challenge occur. In that moment, the coach of the defending team can roll the Challenge Dice to define what happens with the ball. This dice has three possible results: either the player who initiated the challenge recovers the ball, commits a foul or the attacker avoids the defender.
Rolling the Challenge Dice finishes the current turn, so, if the coach wants to consume all their available moves, they have to do it before defining the outcome of the challenge.