Arrest leader of demonstration and member of Greens (7)
I believe the answer is:
collard
'member of greens' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'arrest leader of demonstration' is the wordplay.
'arrest' becomes 'collar' ('collar' can be a synonym of 'arrest').
'leader of' says to take the initial letters.
The first letter of 'demonstration' is 'd'.
'collar'+'d'='COLLARD'
'and' is the link.
Can you help me to learn more?
(Another definition for collard that I've seen is " Cabbage is the answer".)