Projecting rock (4)
I believe the answer is:
'projecting rock' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for crag that I've seen before include "Rough, steep rock face" , "Steep or rugged cliff face" , "Avant-garde" , "Steep rugged rock or cliff" , "Rocky hilltop" .)