Cresting wave (7)
I believe the answer is:
breaker
'cresting wave' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for breaker that I've seen before include "Roller?" , "one stopping, might you say?" , "User of CB radio" , "Wave with white crest" , "A large wave, sounds destructive" .)