Relaxed about a heartless football official (8)
I believe the answer is:
carefree
'relaxed' is the definition.
(thesaurus)
'about a heartless football official' is the wordplay.
'about' becomes 'ca' (abbreviation for 'circa').
'a heartless' means to remove the middle letters.
'football official' becomes 'referee' (referee is a kind of football official).
'referee' with its middle removed is 'refree'.
'ca'+'refree'='CAREFREE'
(Other definitions for carefree that I've seen before include "without worrying?" , "Jaunty" , "Without worry or responsibility" , "Without the burden of responsibility" , "Not worried" .)