Swore at match to journalist below (8)
I believe the answer is:
attested
'swore' is the definition.
(attesting is a kind of swearing)
'at match to journalist below' is the wordplay.
'match' becomes 'test' (as in a test match in cricket).
'to journalist' becomes 'ed' (short for editor).
'below' means one lot of letters go next to another (in a down clue, some letters go below others).
'at'+'test'+'ed'='ATTESTED'
(Other definitions for attested that I've seen before include "Confirmed" , "Affirmed to be true" , "Bore witness to" , "Claimed" , "Provided evidence" .)