Reality produced by fine performance (4)
I believe the answer is:
fact
'reality' is the definition.
(fact is a kind of reality)
'by fine performance' is the wordplay.
'by' says to put letters next to each other.
'fine' becomes 'f' (abbreviation).
'performance' becomes 'act' (act is a kind of performance**).
'f' next to 'act' is 'FACT'.
'produced' is the link.
(Other definitions for fact that I've seen before include "Not fake news!" , "True item; reality" , "It's certainly not fiction" , "Item of truth" , "Piece of information known to be true" .)