Chap running opera (5)
I believe the answer is:
manon
'opera' is the definition.
(Jules Massenet opera)
'chap running' is the wordplay.
'chap' becomes 'man' (chap can mean a man).
'running' becomes 'on' (eg when a machine is running it is on).
'man'+'on'='MANON'
(Other definitions for manon that I've seen before include "Operatic heroine" , "Opera by Massenet" , "Mlle Lescaut (Massenet, Puccini)" , "- - Lescaut (Puccini opera)" .)