Others, into Old English, ripping up Greek plays (8)
I believe the answer is:
Here is my best explanation:
'greek plays' is the definition.
'others into old english ripping up' is the subsidiary indication.
'others' becomes 'rest' (I've seen this in other clues).
'into' indicates putting letters inside.
'old english' becomes 'oe'.
'ripping' becomes 'ai' (A1, term for 'excellent').
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'ai' written backwards gives 'ia'.
'rest' placed inside 'oe' is 'oreste'.
(Other definitions for oresteia that I've seen before include "Play trilogy by Aeschylus, see a riot (anag.)", "Greek plays", "Aeschylus's play trilogy" and "three tragedies for Aeschylus".)