Conclude big match is European (8)
I believe the answer is:
finalise
'conclude' is the definition.
(I've seen this before)
'big match is european' is the wordplay.
'big match' becomes 'final' (I've seen this before).
'european' becomes 'e' (abbreviation e.g. EU).
'final'+'is'+'e'='FINALISE'
(Other definitions for finalise that I've seen before include "Agree on definitive version of something" , "Put an end to, complete" , "Put the last touches to" , "Conclude" , "settle" .)