Attack from journal mostly rejected (4)
I believe the answer is:
raid
'attack' is the definition.
(raid is a kind of attack)
'journal mostly rejected' is the wordplay.
'journal' becomes 'diary' (diary is a kind of journal).
'mostly' means to remove the last letter.
'rejected' is a reversal indicator.
'diary' with its last letter removed is 'diar'.
'diar' back-to-front is 'RAID'.
'from' acts as a link.
(Other definitions for raid that I've seen before include "Maraud" , "Foray, sudden attack" , "Enter a territory and take spoils" , "Rapid surprise attack" , "military operation" .)