Give the fellow the sack - he's a burning fighter! (7)
I believe the answer is:
fireman
'fighter' is the definition.
(I have seen 'Fighter of blaze ' mean 'fireman' so perhaps 'fighter' could also mean 'fireman')
'give the fellow the sack he's a burning' is the wordplay.
I cannot quite see how this works, but
'fellow' could be 'man' (fellow can mean a man) and 'man' is present in the answer.
'sack' could be 'fire' (both can mean to dismiss from a job) and 'fire' is located in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for fireman that I've seen before include "Railway driver's assistant" , "In frame (anag.)" , "Chap with a ladder and hose" , "he puts out at work" , "Fighter of blaze" .)