Holding fast, he deployed cunning (7,2,4)
I believe the answer is:
sleight of hand
'cunning' is the definition.
'holding fast he deployed' is the wordplay.
'deployed' indicates an anagram.
'holding'+'fast'+'he'='holdingfasthe'
'holdingfasthe' is an anagram of 'SLEIGHT-OF-HAND'.
(Other definitions for sleight of hand that I've seen before include "Skilful deception" , "Trickery" , "Manual dexterity in conjuring" , "Legerdemain" , "Doctor or student doctor" .)