Unrealistic hopes of rooks in flight? (7,2,3,3)
I believe the answer is:
castles in the air
'unrealistic hopes' is the definition.
(I've seen this before)
'rooks in flight?' is the wordplay.
'rooks' becomes 'castles' ('castle' can be a synonym of 'rook').
'in flight?' becomes 'intheair' (I can't explain this - if you can you should give a lot more credence to this answer).
'castles'+'intheair'='CASTLES IN THE AIR'
'of' is the link.
Can you help me to learn more?
(Other definitions for castles in the air that I've seen before include "rooks circling overhead" , "Unrealistic hopes" , "flying fortresses" , "daydreams" , "dreamy schemes" .)