Late start and delay, then be ready to attack (3,2,4)
I believe the answer is:
lie in wait
'be ready to attack' is the definition.
'late start and delay' is the wordplay.
'late start' becomes 'liein' (I can't explain this - if you can you should give a lot more credence to this answer).
'and' means one lot of letters go next to another.
'delay' becomes 'wait' (synonyms).
'liein'+'wait'='LIE IN WAIT'
'then' is the link.
Can you help me to learn more?
(Other definitions for lie in wait that I've seen before include "remain hidden while preparing to attack" , "Be ready to surprise" , "Plan for ambush" , "prepared for attack!" , "as some bushwhackers do" .)