Sack Liberal leaving for dire crusade (10)
I believe the answer is:
pilgrimage
'crusade' is the definition.
(thesaurus)
'sack liberal leaving for dire' is the wordplay.
I cannot really see how this works, but
'liberal' could be 'l' (abbreviation) and 'l' is found within the answer.
'dire' could be 'grim' (I've seen this before) and 'grim' is located in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for pilgrimage that I've seen before include "Religiously inspired journey" , "Holy journey" , "special journey?" , "What Chaucer,s travellers were engaged upon" , "journey to shrine" .)