Answer includes a repeat fixture (6)
I believe the answer is:
replay
'repeat fixture' is the definition.
(I've seen this before)
'answer includes a' is the wordplay.
'answer' becomes 'reply' (synonyms).
'includes' indicates putting letters inside.
'reply' going around 'a' is 'REPLAY'.
(Other definitions for replay that I've seen before include "A cup tie; clip shown over and over" , "Hold match again" , "Repeated match" , "A restaged match" , "Repeat recording of part of game" .)