Criminal offence of a group in court (7)
I believe the answer is:
perjury
This clue is a double definition.
'criminal offence' is the first definition.
'a group in court' is the second definition.
'of' acts as a link.
(Other definitions for perjury that I've seen before include "Crime of lying under oath" , "Offence of lying under oath" , "Lying in court" , "False swearing" , "Telling lies in court under oath" .)