Some regular anime series upset study group (7)
I believe the answer is:
seminar
'study group' is the definition.
(I've seen this before)
'some regular anime series upset' is the wordplay.
'some' indicates the answer is hidden within the clue (some parts of the word are used).
'upset' shows that the letters should be reversed in order.
'ranimes' is hidden within 'regular anime series'.
'ranimes' in reverse letter order is 'SEMINAR'.
(Other definitions for seminar that I've seen before include "Meeting for study" , "workshop" , "Student discussion group - remains (anag)" , "Tutorial group meeting" , "Teaching meeting, conference" .)