They are out on cold nights showing courage, rest having been disturbed (8)

'they are out on cold nights' is the definition.
I don't know anything about this answer so I can't tell whether it can be defined by this definition.

'courage rest having been disturbed' is the wordplay.
I cannot really see how this works, but
'courage' could be 'grit' (I've seen this before) and 'grit' is found within the answer.
an anagram of 'rest' is 'ters' which is located in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).

'showing' acts as a link.

Can you help me to learn more?