French city badly walled by the French (5)
I believe the answer is:
lille
'french city' is the definition.
(Lille is a city in France)
'badly walled by the french' is the wordplay.
I cannot really see how this works, but
'badly' could be 'ill' ('ill' can be adverbial as in 'ill-advised') and 'ill' is present in the answer.
'the french' could be 'le' ('the' in French) and 'le' is found within the answer.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for lille that I've seen before include "Stop before Paris" , "[FRANCOPHOBIA] would prevent you appreciating it" , "N. French city" , "University city in French Flanders" , "City of N. France" .)