Bad hearing and poor visibility led to the rail crash (8)
I believe the answer is:
mistrial
'bad hearing' is the definition.
(I've seen this before)
'poor visibility led to the rail crash' is the wordplay.
'poor visibility led' becomes 'mis' (I can't explain this - if you can you should believe this answer much more).
'to the' becomes 't' (the is pronounced as a 't' sound in some dialects).
'crash' is an anagram indicator.
'rail' with letters rearranged gives 'rial'.
'mis'+'t'+'rial'='MISTRIAL'
'and' is the link.
Can you help me to learn more?
(Other definitions for mistrial that I've seen before include "Court hearing invalidated by error" , "Failed court action" , "When it's declared, the case must be heard again" , "Inconclusive or invalid court proceedings" , "damaged hearing?" .)