Runs over to help attack (4)
I believe the answer is:
raid
'attack' is the definition.
(I know that Raid is a type of attack)
'runs over to help' is the wordplay.
'runs' becomes 'r' (cricket abbreviation).
'over' means one lot of letters go next to another.
'to help' becomes 'aid' ('aid' can be a synonym of 'help').
'r'+'aid'='RAID'
(Other definitions for raid that I've seen before include "Rapid surprise attack" , "Smash-and-grab?" , "Go on the attack" , "Sudden short attack" , "Assault, attack" .)