Bats maul predator which is hard to attack (6-6)
I believe the answer is:
armour-plated
'is hard to attack' is the definition.
(something armour-plated is hard to attack)
'bats maul predator' is the wordplay.
'bats' is an anagram indicator (slang for mad).
'maul'+'predator'='maulpredator'
'maulpredator' anagrammed gives 'ARMOUR-PLATED'.
'which' acts as a link.
(Other definitions for armour-plated that I've seen before include "Well-protected" , "Having a hard defensive skin" , "Bulletproof" .)