Group about to follow rotter (5)
I believe the answer is:
cadre
'group' is the definition.
The answer is an example.
'about to follow rotter' is the wordplay.
'about' becomes 're' (regarding).
'to follow' means one lot of letters go next to another (some letters go after or follow others).
'rotter' becomes 'cad' (a cad is a dishonourable person).
're' after 'cad' is 'CADRE'.
(Other definitions for cadre that I've seen before include "Inner group of activists in a revolutionary party" , "Small group of people trained for a purpose" , "Nucleus, corps" , "activist group" , "revolutionary cell" .)