Gang member’s boss going under cover (8)
I believe the answer is:
skinhead
'gang member's' is the definition.
'boss going under cover' is the wordplay.
'boss' becomes 'head' ('head' can be a synonym of 'boss').
'going under' says to put letters next to each other.
'cover' becomes 'skin' (skin is a kind of cover**).
'head' put after 'skin' is 'SKINHEAD'.
(Other definitions for skinhead that I've seen before include "Bald member of a youth faction" , "hooligan" , "voluntary exhibitor of 11" , "Intimidating hairstyle, closely shaved" , "rough-looking" .)