Subject those people to the ultimate in abuse (5)
I believe the answer is:
theme
'subject' is the definition.
(theme can mean a topic or subject)
'those people to the ultimate in abuse' is the wordplay.
'those people' becomes 'them' ('they' refers to a group of people).
'to the ultimate in' suggests the final letters (take the ultimate ie last letter).
The final letter of 'abuse' is 'e'.
'them'+'e'='THEME'
(Other definitions for theme that I've seen before include "Subject of a talk or piece of writing" , "Motif that's repeated" , "Motif - 4 across" , "Subject matter, motif" , "sort of tune" .)