The crime of a hard-hearted lad (5)
I believe the answer is:
arson
'the crime' is the definition.
(I've seen this before)
'a hard-hearted lad' is the wordplay.
'hearted' says to take the centre.
'lad' becomes 'son'.
The central letters of 'hard' are 'ar'.
'ar'+'son'='ARSON'
'of' acts as a link.
(Other definitions for arson that I've seen before include "The act of firing" , "Crime of fire-setting (5)" , "Criminal activity" , "Sonar (anag.)" , "major crime" .)