Scab caused by blow wave (13)
I believe the answer is:
strikebreaker
'scab' is the definition.
('strikebreaker' can be a synonym of 'scab')
'blow wave' is the wordplay.
'blow' becomes 'strike' (strike is a kind of blow**).
'wave' becomes 'breaker' (breaker is a kind of wave).
'strike'+'breaker'='STRIKEBREAKER'
'caused by' acts as a link.
(Other definitions for strikebreaker that I've seen before include "One won't come out" , "Scab" , "Blackleg" .)