Sack fellow first responder (7)
I believe the answer is:
fireman
'first responder' is the definition.
The answer and definition can be both people as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'sack fellow' is the wordplay.
'sack' becomes 'fire' (both can mean to dismiss from a job).
'fellow' becomes 'man' (fellow can mean a man).
'fire'+'man'='FIREMAN'
Can you help me to learn more?
(Other definitions for fireman that I've seen before include "Railway driver's assistant" , "who does a rushed job on tender?" , "Conflagration fighter" , "he puts out at work" , "Red engine driver" .)