Be ready to attack untrue statement during delay (3,2,4)
I believe the answer is:
lie in wait
'be ready to attack' is the definition.
'untrue statement during delay' is the wordplay.
'untrue statement' becomes 'lie'.
'during' becomes 'in' (I've seen this in other clues).
'delay' becomes 'wait' ('wait' can be a synonym of 'delay').
'lie'+'in'+'wait'='LIE IN WAIT'
(Other definitions for lie in wait that I've seen before include "hover" , "remain hidden while preparing to attack" , "Plan to attack" , "Set an ambush" , "Prepare to attack" .)