The real jerks hit hard (7)
I believe the answer is:
leather
'hit hard' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'the real jerks' is the wordplay.
'jerks' indicates an anagram (I've seen 'jerk' mean this).
'the'+'real'='thereal'
'thereal' is an anagram of 'LEATHER'.
Can you help me to learn more?
(Other definitions for leather that I've seen before include "Cured animal hide" , "Whip" , "polish" , "Treated animal skin" , "Tanned animal skin" .)