To scrutinise the lad on return is injurious to the reputation (7)
I believe the answer is:
scandal
'injurious to the reputation' is the definition.
I can't judge whether this definition defines the answer.
'to scrutinise the lad on return' is the wordplay.
'to scrutinise' becomes 'scan' (I've seen this before).
'on return' says the letters should be written in reverse.
'lad' back-to-front is 'dal'.
'scan'+'dal'='SCANDAL'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for scandal that I've seen before include "Public disgrace" , "Rumour, gossip" , "Outrageous event" , "dirt" , "Something shameful or disgraceful, often public" .)