Large case of alcohol causing death (5)
I believe the answer is:
fatal
'causing death' is the definition.
(I've seen this before)
'large case of alcohol' is the wordplay.
'large' becomes 'fat' (I've seen this in other clues).
'case of' suggests removing the centre (outsides of).
'alcohol' with its middle removed is 'al'.
'fat'+'al'='FATAL'
(Other definitions for fatal that I've seen before include "critical" , "Causing death, say accident" , "Death-dealing" , "Leading to disaster" , "Causing or leading up to death" .)