In a heartless way, seized and released grouse (6)
I believe the answer is:
griped
'in a heartless way seized and released' is the definition.
I can't judge whether this definition defines the answer.
'grouse' is the wordplay.
I cannot really understand how this works, but
'grouse' could be 'gripe' (synonyms) and 'gripe' is found in the answer.
A single letter 'd' remains which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for griped that I've seen before include "Complained persistently" , "Moaned constantly" .)