Damage volunteers with a rum cocktail (6)
I believe the answer is:
Here is my best explanation:
'damage' is the definition.
(I have seen 'Emotional damage ' mean 'trauma' so perhaps 'damage' could also mean 'trauma')
'volunteers with a rum cocktail' is the wordplay.
'volunteers' becomes 'ta' (abbreviation for Territorial Army).
'with' means one lot of letters goes inside another.
'cocktail' indicates an anagram.
'arum' is an anagram of 'raum'.
'ta' placed around 'raum' is 'TRAUMA'.
(Other definitions for trauma that I've seen before include "dreadful shock!", "Psychological 23", "Wound - emotional shock", "Emotional upset", "Deep distress; injury", "Emotional shock or physical injury", "Very distressing experience", "Emotional shock, long-lasting", "Nervous shock" and "Distressing experience".)