Record single back around number four in chart (5)
I believe the answer is:
enrol
'record' is the definition.
(I've seen this before)
'single back around number four in chart' is the wordplay.
'single' becomes 'lone' (synonyms).
'back' says the letters should be written backwards.
'around' indicates putting letters inside.
'number four in chart' becomes 'r' (4th letter of 'chart').
'lone' back-to-front is 'enol'.
'enol' going around 'r' is 'ENROL'.
(Other definitions for enrol that I've seen before include "Sign on, register" , "Sign up (member)" , "Recruit" , "Join up, sing on" , "Register officially" .)