Attempt to include old play (7)
I believe the answer is:
tragedy
'play' is the definition.
(I have seen 'Serious play ' mean 'tragedy' so perhaps 'play' could also mean 'tragedy')
'attempt to include old' is the wordplay.
'attempt to' becomes 'try' (I've seen this in other clues).
'include' is an insertion indicator.
'old' becomes 'aged' (similar in meaning).
'try' enclosing 'aged' is 'TRAGEDY'.
(Other definitions for tragedy that I've seen before include "Calamity as in sad play" , "Huge blow" , "Hamlet, say" , "Calamity, disaster" , "shocking event" .)