A cry of pain from leverets outside - they never heard these hunters coming. (4)
I believe the answer is:
owls
'they never heard these hunters coming' is the definition.
The definition suggests an adverb but the answer is not.
'a cry of pain from leverets outside' is the wordplay.
'a cry of pain' becomes 'ow' (exclamation of pain).
'from' means one lot of letters go next to another.
'outside' means to remove the middle letters.
'leverets' with its centre removed is 'ls'.
'ow'+'ls'='OWLS'
Can you help me to learn more?
(Other definitions for owls that I've seen before include "Wise old birds - quite slow" , "Slow kind of birds" , "Nocturnal birds" , "Nocturnal hooters?" , "Slow (anag) -- birds of prey" .)