Strutting of piles beside river (8)
I believe the answer is:
cocksure
'strutting of' is the definition.
I can't judge whether this defines the answer.
'piles beside river' is the wordplay.
'piles' becomes 'cocks' (I can't explain this - if you can you should give a lot more credence to this answer).
'beside' says to put letters next to each other (I've seen this in other clues).
'river' becomes 'Ure' (river in Yorkshire).
'cocks'+'ure'='COCKSURE'
Can you help me to learn more?
(Other definitions for cocksure that I've seen before include "Offensively confident" , "Foolishly over-confident" , "Arrogantly certain" , "Showing arrogance" , "Irritatingly self-confident" .)