Forceful, macho types held in check (8)
I believe the answer is:
vehement
'forceful' is the definition.
(thesaurus)
'macho types held in check' is the wordplay.
'macho types' becomes 'hemen'.
'held in' is an insertion indicator.
'check' becomes 'vet' (I've seen this before).
'hemen' placed inside 'vet' is 'VEHEMENT'.
(Other definitions for vehement that I've seen before include "Emphatic, intense" , "Violent" , "heated" , "Vet he-men showing strong feeling" , "Of speech, intense and forceful" .)