Lights not working inside of hall (5)
I believe the answer is:
Here is my best explanation:
'lights' is the definition.
(I've seen this before)
'not working inside of hall' is the subsidiary indication.
'not working' becomes 'off' (I've seen this in other clues).
'inside of' says to take the centre.
The centre of 'hall' is 'al'.
(Other definitions for offal that I've seen before include "Refuse - guts", "Rejected parts of a carcase", "Refuse - edible entrails of animal", "Entails and organs of animals, rubbish", "Inner organs used for food", "Organs as food", "Rubbishy bits of animal flesh", "Waste of carcase", "Heart, liver, kidney etc" and "Butcher's leftovers".)