The side needs changing in a month - this group decides (4)
I believe the answer is:
jury
This clue could be a double definition.
'the side' is the first definition.
The answer and definition can be both groups as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'changing in a month this group decides' is the second definition.
The definition and answer can be both groups as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'needs' acts as a link.
Can you help me to learn more?
(Other definitions for jury that I've seen before include "Body of competition judges" , "Committee of examiners" , "Group sworn to deliver verdict in court" , "Panel of twelve" , "Judging panel" .)