Surprise attack (4)
(Other definitions for inroad that I've seen before include "Sudden attack made into a country" , "Offensive" , "Ordain (anag.)" , "Foray" , "One's intrusive" .)
'surprise attack' is the definition.
(ambush is a kind of surprise attack)
This is the entire clue.
(Other definitions for ambush that I've seen before include "Wait in hiding to attack" , "Lie in wait; trap" , "Attack from concealment" , "Waylay" , "Lie in wait and attack" .)
(Other definitions for raid that I've seen before include "Finch and Bronson starred in . . . . On Entebbe" , "Rapid surprise attack" , "Sudden and surprise attack" , "A sudden attack or incursion" , "Sudden short attack" .)