He's smart, leaving the scene of operations (3)
I believe the answer is:
fop
'he's smart' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'leaving the scene of operations' is the wordplay.
'leaving' indicates the answer is hidden within the clue (the answer must leave the confines of the clue).
'FOP' can be found hidden inside 'scene of operations'.
Can you help me to learn more?
(Other definitions for fop that I've seen before include "A dandy like Beau Brummel" , "A man much concerned with his appearance, a dandy" , "Man excessively concerned with fashion" , "he enjoys the finest dressing" , "'Dandy, coxcomb (3)'" .)