Block in path, so bikers turned back (6)
I believe the answer is:
kibosh
'block' is the definition.
('kibosh' can be a synonym of 'block')
'in path so bikers turned back' is the wordplay.
'in' says the answer is hidden in the clue.
'turned back' is a reversal indicator.
'hsobik' is hidden within 'path so bikers'.
'hsobik' backwards is 'KIBOSH'.
(Other definitions for kibosh that I've seen before include "Finish off" , "Nonsense (slang)" , "Hibs O.K. (anag) - put a stop to" , "Terminate" , "Put the mockers on" .)