Leaders of Coldstream Guards defend everyone in work (7)
I believe the answer is:
calling
'work' is the definition.
(someone's career or vocation)
'leaders of coldstream guards defend everyone in' is the wordplay.
'leaders of' suggests taking the first letters.
'defend' means one lot of letters goes inside another.
'everyone' becomes 'all' (all people).
The first letters of 'coldstream guards' is 'cg'.
'all'+'in'='allin'
'cg' placed around 'allin' is 'CALLING'.
(Other definitions for calling that I've seen before include "Urge to follow a particular career" , "Running a bingo game" , "visiting" , "Predicting the outcome" , "Occupation" .)