Are keeping it back from him (5)
I believe the answer is:
artie
'him' is the definition.
'are keeping it back' is the wordplay.
'keeping' means one lot of letters goes inside another.
'back' says the letters should be written in reverse.
'it' reversed gives 'ti'.
'are' going around 'ti' is 'ARTIE'.
'from' acts as a link.
(Other definitions for artie that I've seen before include "- Shaw, US jazz clarinettist and bandleader" , "Guy" , "Shaw, perhaps?" , "-- Shaw, jazz musician" , "Man" .)