Chief ruthlessly held back gang's territory (4)
I believe the answer is:
turf
'gang's territory' is the definition.
(I've seen this in another clue)
'chief ruthlessly held back' is the wordplay.
'held' says the answer is hidden in the clue.
'back' shows that the letters should be reversed in order.
'frut' can be found hidden inside 'chief ruthlessly'.
'frut' in reverse letter order is 'TURF'.
(Other definitions for turf that I've seen before include "Cover over with grass" , "Gang's territory" , "This accountant is a bookie" , "Horseracing as an industry" , "Some 19 dn; chuck (out)" .)