Confirm an international match is to be broadcast (6)
I believe the answer is:
attest
'confirm' is the definition.
(I've seen this before)
'an international match is to be broadcast' is the wordplay.
'an international match' becomes 'test' (I've seen this before).
'is to' means one lot of letters go next to another (I've seen this in other clues).
'be broadcast' becomes 'at' (I can't justify this - if you can you should believe this answer much more).
'test' after 'at' is 'ATTEST'.
Can you help me to learn more?
(Other definitions for attest that I've seen before include "Vouch for" , "Adjure" , "Swear to" , "Bear formal witness to, give evidence" , "Make evident" .)