He's involved in crafty act (5)
I believe the answer is:
cheat
'he's involved in crafty act' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'he's involved in crafty act' is the wordplay.
'involved in' means one lot of letters goes inside another.
'crafty' indicates anagramming the letters.
'act' with letters rearranged gives 'cat'.
'he' put within 'cat' is 'CHEAT'.
Can you help me to learn more?
(Other definitions for cheat that I've seen before include "Trick or swindle" , "Two-time" , "Play dishonestly" , "Teach? (Anag)" , "Two-timer" .)