One boy in Lyon, not on shore leave (7)
I believe the answer is:
liberty
'shore leave' is the definition.
('liberty' can be a synonym of 'shore leave')
'one boy' is the wordplay.
'one' becomes 'li' (I've seen this in other clues).
'boy' becomes 'berty' (**).
'li'+'berty'='LIBERTY'
'in lyon not on' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for liberty that I've seen before include "Independence" , "Lack of constraint, restraint" , "Freedom from slavery" , "cheek" , "Act of undue intimacy" .)