Brute was wrong to prove false (5)
I believe the answer is:
rebut
'prove false' is the definition.
(I've seen this in another clue)
'brute was wrong' is the wordplay.
'was wrong' indicates an anagram (I've seen 'is wrong' mean this).
'brute' with letters rearranged gives 'REBUT'.
'to' is the link.
(Other definitions for rebut that I've seen before include "Contradict or disprove" , "Quash" , "Check" , "Prove to be false or incorrect" , "Overthrow by argument or proof" .)