Forceful tough guys kept in check (8)
I believe the answer is:
vehement
'forceful' is the definition.
(I've seen this before)
'tough guys kept in check' is the wordplay.
'tough guys' becomes 'hemen' (I've seen this in another clue).
'kept in' indicates putting letters inside.
'check' becomes 'vet' (I've seen this in other clues).
'hemen' put into 'vet' is 'VEHEMENT'.
(Other definitions for vehement that I've seen before include "Irish symbol" , "Showing strong feeling, like even them" , "Fervid" , "Forceful, ardent" , "Showing strong feeling, intense in speech" .)