Hide cause of BT failing (9)
I believe the answer is:
obfuscate
'hide' is the definition.
(I've seen this before)
'cause of bt failing' is the wordplay.
'failing' is an anagram indicator.
'cause'+'of'+'bt'='causeofbt'
'causeofbt' anagrammed gives 'OBFUSCATE'.
(Other definitions for obfuscate that I've seen before include "Darken or obscure something" , "Darken - bewilder" , "Dim" , "Make unintelligible" , "Make confused" .)