The felony of a hard hearted-lad? (5)
I believe the answer is:
arson
'the felony' is the definition.
(I've seen this in another clue)
'hard hearted-lad?' is the wordplay.
'hearted' means to look at the middle letters.
'lad?' becomes 'son' (lad can informally mean a young boy).
The centre of 'hard' is 'ar'.
'ar'+'son'='ARSON'
'of a' acts as a link.
(Other definitions for arson that I've seen before include "Pyromaniac's crime" , "serious offence" , "criminal fire-raising" , "Act of a pyromaniac" , "Malicious fire-lighting" .)