Befuddle by taking top off oar (5)
I believe the answer is:
addle
'befuddle' is the definition.
(I've seen this in another clue)
'taking top off oar' is the wordplay.
'taking top off' means to remove the first letter.
'oar' becomes 'paddle' (paddle is a kind of oar).
'paddle' with its initial letter taken off is 'ADDLE'.
'by' acts as a link.
(Other definitions for addle that I've seen before include "Make rotten" , "Confuse - decay" , "Scramble" , "Muddle or confuse" , "Rot" .)