Witness at cricket match (6)
I believe the answer is:
attest
'witness' is the definition.
(I've seen this before)
'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 "Verify" , "Give sworn evidence" , "Provide firm evidence" , "Confirm to be true" , "Give evidence in a court of law" .)