Obscure pop group (4)
I believe the answer is:
blur
This clue is a double definition.
'obscure' is the first definition.
('blur' can be a synonym of 'obscure')
'pop group' is the second definition.
(Other definitions for blur that I've seen before include "Make or become indistinct" , "Indistinct mark" , "Hazy or indistinct image" , "Ill-defined smear" , "Rock band - make less clear" .)