Former wrong to get one on theft by threat (9)
I believe the answer is:
extortion
'theft by threat' is the definition.
I can't tell whether this definition defines the answer.
'former wrong to get one on' is the wordplay.
'former' becomes 'ex' (prefix meaning former or onetime).
'wrong' becomes 'tort' (legal term).
'to get' is a charade indicator (letters next to each other).
'one' becomes 'i' (Roman numeral).
'ex'+'tort'+'i'+'on'='EXTORTION'
Can you help me to learn more?
(Other definitions for extortion that I've seen before include "Blackmail" , "Extraction of money with menaces" , "The obtaining of money by force or threat" .)