Chap, old, playing popular instrument (8)
I believe the answer is:
mandolin
'instrument' is the definition.
(mandolin is a kind of instrument)
'chap old playing popular' is the wordplay.
'chap' becomes 'man' (I've seen this before).
'playing' is an anagram indicator.
'popular' becomes 'in'.
'old' anagrammed gives 'dol'.
'man'+'dol'+'in'='MANDOLIN'
(Other definitions for mandolin that I've seen before include "Plucked instrument" , "Musical instrument like a small lute" , "one's deployed in the kitchen" , "Lute-like instrument" , "Instrument resembling a lute" .)