Swindler against leaving extremely crowded place (7)
I believe the answer is:
rookery
'crowded place' is the definition.
The definition and answer can be both locations as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'swindler against leaving extremely' is the wordplay.
'swindler' becomes 'rooker' (I've seen this in another clue).
'against' says to put letters next to each other.
'leaving extremely' becomes 'y' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'rooker'+'y'='ROOKERY'
Can you help me to learn more?
(Other definitions for rookery that I've seen before include "Seal, penguin, colony" , "Breeding colony of birds, also of seals or turtles" , "Noisy bird colony" , "Colony of penguins or seals" , "breeding ground" .)