Betting journalist was rushed (4)
I believe the answer is:
'rushed' is the definition.
('speed' can be a synonym of 'rush')
'betting journalist' is the wordplay.
'betting' becomes 'sp'.
'journalist' becomes 'ed' (short for editor).
'was' acts as a link.
(Other definitions for sped that I've seen before include "Raced, hurried" , "Travelled quickly" , "Hastened" , "Rushed" , "Moved quickly" .)