Fool to drop off a criminal with hostage (9)
I believe the answer is:
kidnapper
'criminal with hostage' is the definition.
I can't tell whether this defines the answer.
'fool to drop off a' is the wordplay.
'fool' becomes 'kid' (kidding is a kind of fooling).
'to drop off' becomes 'nap' (drop off can mean to sleep).
'a' becomes 'per' (eg 'one a day' means 'one per day').
'kid'+'nap'+'per'='KIDNAPPER'
Can you help me to learn more?
(Other definitions for kidnapper that I've seen before include "Paris, for example" , "One wrongly takes" , "Holder of a person for ransom" , "Ransom demander" , "Captor of a human being, for ransom" .)