A card can be Ready or Exhausted.
When a rule says to exhaust a card, it means to mark that card as exhausted (not ready).

When a rule says to ready a card, it means the card should no longer be marked as exhausted.
When a rule refers to ‘a ready card’ it means only a card in the ready state can be used for that rule.
An exhausted card can:
▪        use their abilities (unless the ability specifies the card must be ready, or requires you to exhaust the card as a cost)
▪        be boosted by a ‘player boost’ action
▪        be the defending card during attack resolution
An exhausted card cannot:
▪        Move (although another ready card can swap positions with an exhausted card by moving into its space)
▪        Pass the ball or receive a pass
▪        be the attacking card during attack resolution