Watching international cricket, declare (6)
I believe the answer is:
attest
'declare' is the definition.
(attesting is a kind of declaring)
'watching international cricket' is the wordplay.
'watching' becomes 'at' (e.g. watching a tennis match means you are at it).
'international cricket' becomes 'test' (test match).
'at'+'test'='ATTEST'
(Other definitions for attest that I've seen before include "Give evidence - sounds a trial" , "Declare to be true or genuine" , "Act as witness" , "Provide proof of, declare to be true (6)" , "Give proof" .)