Blade protected by cardboard (3)
I believe the answer is:
oar
'blade' is the definition.
(blade is the word for oar in competitive rowing)
'protected by cardboard' is the wordplay.
'protected by' indicates the answer is hidden within the clue.
'OAR' is hidden within 'cardboard'.
(Other definitions for oar that I've seen before include "Crew member" , "Sportsman" , "Rower's implement" , "Use it to move a boat" , "Propelling pole" .)