Group studying remains in ruin (7)
I believe the answer is:
seminar
'group studying' is the definition.
(study group at a university)
'remains in ruin' is the wordplay.
'in ruin' indicates an anagram (I've seen 'in ruins' mean this).
'remains' with letters rearranged gives 'SEMINAR'.
(Other definitions for seminar that I've seen before include "Meeting for exchange of ideas" , "Study group on specific subject" , "Group discussing" , "Training meeting" , "Symposium" .)