Harry's in good condition taking in heart of Sussex (6)
I believe the answer is:
hassle
'harry's' is the definition.
(I know this)
'in good condition taking in heart of sussex' is the wordplay.
'in good condition' becomes 'hale' (I've seen this in another clue).
'taking in' means one lot of letters goes inside another.
'heart of' says to take the centre.
The centre of 'sussex' is 'ss'.
'hale' placed around 'ss' is 'HASSLE'.
(Other definitions for hassle that I've seen before include "Informally, annoy or harass" , "Informally, annoyance or quarrel" , "Annoying trouble" , "Bother, fuss" , "Harass - bother" .)