Commentary on Sections Part 1, Chapter 1 – Offence of Domestic Abuse Section 12: Defence on the grounds of reasonableness
This section provides that it is a defence for the accused to show that the course of behaviour was, in the particular circumstances, reasonable.  This may apply where, for example, the accused acted to prevent their partner from associating with certain persons or frequenting certain places if they are recovering from alcohol or drug addiction or to restrict their freedom of movement for their own safety due to the effects of suffering from dementia.  It is expected the defence would apply in very limited circumstances.
Subsection (2) allows for the accused to adduce evidence that is enough to raise an issue as to whether the course of behaviour was reasonable, with the prosecution then needing to disprove this version of events.
Nothing in this section affects the broader requirement for the prosecution to prove beyond reasonable doubt that the offence has been committed.