Fox hurt by youth lacking boundaries (8)
I believe the answer is:
outsmart
'fox' is the definition.
(I've seen this before)
'hurt by youth lacking boundaries' is the wordplay.
'hurt' becomes 'smart' (synonyms).
'by' means one lot of letters go next to another.
'lacking boundaries' indicates the central letters (the boundaries of the word are removed).
The middle letters of 'youth' are 'out'.
'smart' put after 'out' is 'OUTSMART'.
(Other definitions for outsmart that I've seen before include "Win by clever thinking" , "Fool" , "Outmanoeuvre cleverly" , "Defeat by skillful maneuvering" , "Excel in cleverness" .)