Fit ground inside city? That’s clever (5)
I believe the answer is:
nifty
'that's clever' is the definition.
(I've seen this in another clue)
'fit ground inside city?' is the wordplay.
'ground' is an anagram indicator ('grind' the letters into a new form).
'inside' indicates putting letters inside.
'city?' becomes 'ny' (short for New York).
'fit' anagrammed gives 'ift'.
'ift' put inside 'ny' is 'NIFTY'.
(Other definitions for nifty that I've seen before include "Smart" , "Really good (slang)" , "Fine (slang)" , "Slick" , "Particularly good (informal)" .)