They hit one without any reason (8)
I believe the answer is:
crackers
'they' is the definition.
Both the answer and definition are plural nouns.
Perhaps you can see an association between them that I can't see?
'hit one without any reason' is the wordplay.
'hit' becomes 'crack' (cracking is a kind of hitting).
'one without any reason' becomes 'ers' (I am not sure about this - if you are sure you should believe this answer much more).
'crack'+'ers'='CRACKERS'
Can you help me to learn more?
(Other definitions for crackers that I've seen before include "Nutty - biscuits" , "one may find them on the table tomorrow" , "Mad - fireworks" , "Thin biscuits for cheese" , "Pulled at parties!" .)