Shock tactics initially revealed in tabloid newspaper (4)
I believe the answer is:
stun
'shock' is the definition.
(both can mean to surprise)
'tactics initially revealed in tabloid newspaper' is the wordplay.
'initially' suggests taking the first letters.
'revealed in' indicates putting letters inside.
'tabloid newspaper' becomes 'Sun' (The Sun is a tabloid newspaper).
The initial letter of 'tactics' is 't'.
't' inserted inside 'sun' is 'STUN'.
(Other definitions for stun that I've seen before include "Knock out temporarily" , "Render insensitive" , "Concuss, stupefy" , "cause amazement" , "Daze, paralyse" .)