Discharged from unsatisfactory service, going away (3,3)
I believe the answer is:
let off
'discharged from unsatisfactory' is the definition.
I can't judge whether this definition defines the answer.
'service going away' is the wordplay.
I cannot really see how this works, but
'service' could be 'let' (type of tennis serve) and 'let' is found in the answer.
'going' could be 'off' (I've seen this in another clue) and 'off' is present in the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for let off that I've seen before include "Cause to explode or excuse from duties" , "Allow to go free; discharge" , "Set free without charge" , "Go easy on" , "impose no punishment at all?" .)