Shock when rocker perhaps goes topless (4)
I believe the answer is:
hair
'shock' is the definition.
(shock can mean a mass of hair)
'rocker perhaps goes topless' is the wordplay.
'rocker perhaps' becomes 'chair' (rocker is a kind of chair).
'goes topless' means to remove the first letter (I've seen 'went topless' mean this).
'chair' with its first letter removed is 'HAIR'.
'when' is the link.
(Other definitions for hair that I've seen before include "Tresses" , "Threadlike strands growing from the skin" , "Penitent's shirt material" , "Nineteen sixties musical; filament" , "Filaments growing on the epidermis" .)