Declare at cricket match (6)
I believe the answer is:
attest
'declare' is the definition.
(I know that attest is a more specific form of the action declare)
'at cricket match' is the wordplay.
'cricket match' becomes 'test' (a test is a kind of cricket match).
'at'+'test'='ATTEST'
(Other definitions for attest that I've seen before include "Declare (that something is the case)" , "Give evidence - sounds a trial" , "Vouch for" , "Give proof" , "Declare to be true or genuine" .)