The defender may make as many actions as they wish. The actions they may make are:

Play cards: You may pay the energy cost on a card in your hand to play it to one of the 6 spaces on your side of the pitch. You may also play a card into a space which is already occupied by another card. The card being replaced is put into the discard pile. Cards with the FAST ability can be played during this phase.
Use abilities: Many cards have abilities that can be used during play. Some may require a cost to use them (e.g. spending energy tokens, exhausting the card, or discarding cards from your hand). Each ability may only be used once per round.
Move: You can exhaust a card to move it to an orthogonally adjacent space. If another card is already in that space, you can have them swap positions (the card being moved from the desired space is not exhausted).

Goalkeepers cannot be played during this phase.
If an action exhausts or stuns the card with possession of the ball, that is called a ‘loose ball’.
When the defending user is done taking actions, this phase ends.