How did she come to be assaulted?
It is difficult to say really.
Certainly on the case as you present it you would have a defence because you were acting lawfully to defend her.
To charge you with affray there would need to be some evidence that you acted without a lawful reason.
But the problem is I suppose that you don't know how this came about. It is quite unlikely somebody just attacked her for no reason at all without any provocation.
It isn't particularly standard practice. You don't see many affrays any more.
But it is something they are entitled to do.
I'm sorry you are in this position as I suppose she has escaped consequences entirely.
Can I clarify anything for you?
The lesson is never get involved in your partner's disputes. I know that men are generally socialised to protect women but it is always the cause of problems for them. I have lost count of the number of perfectly law abiding men who would never have ended up in the dock if they hadn't been sorting out their partner's issues.
Interestingly the ladies never join them in the dock.
However, if you haven't been charged with affray then I wouldn't expect it. It is pretty rare that is used now.
They may use S4 public order possibly but you don't see many affrays now
That isn't always a good thing. Essentially all the money is being spent investigating false allegations of historical sexual abuse.