Bound to adopt measure — thus cyclist protected? (8)
I believe the answer is:
helmeted
'thus cyclist protected?' is the definition.
(wearing a helmet)
'bound to adopt measure' is the wordplay.
'bound' becomes 'held' (bound can mean held or contained).
'to adopt' is an insertion indicator.
'measure' becomes 'mete' (meting things out is measuring them out).
'held' going around 'mete' is 'HELMETED'.
(Other definitions for helmeted that I've seen before include "Wearing a protective hat" , "Having head protection" .)