Very popular track containing say A sharp (8)
I believe the answer is:
vinegary
'sharp' is the definition.
(sharp in taste)
'very popular track containing say a' is the wordplay.
'very' becomes 'v' (abbreviation).
'popular' becomes 'in' ('in' can mean trendy).
'track' becomes 'ry' (abbreviation for railway).
'containing' is an insertion indicator.
'say' becomes 'eg' (both can mean for example).
'in'+'ry'='inry'
'eg'+'a'='ega'
'inry' enclosing 'ega' is 'inegary'.
'v'+'inegary'='VINEGARY'
(Other definitions for vinegary that I've seen before include "Peevish" , "Acerbic" , "Sour tasting" , "bitter" .)