Reckless old man imprisons sappers? Wrong (9)
I believe the answer is:
daredevil
'reckless' is the definition.
(thesaurus)
'old man imprisons sappers? wrong' is the wordplay.
'old man' becomes 'dad' ('dad' can be a synonym of 'old man').
'imprisons' indicates putting letters inside.
'sappers?' becomes 're' (Royal Engineers).
'wrong' becomes 'evil' ('evil' is associated in meaning with 'wrong'**).
'dad' placed around 're' is 'dared'.
'dared'+'evil'='DAREDEVIL'
(Other definitions for daredevil that I've seen before include "Lover of danger" , "Reckless person who enjoys danger" , "Seeker after danger" , "Dread evil, being a reckless person" , "Lived, dear like rckless adventurer" .)