See Yorkshire river beside event in Sheffield, say (5,5)
I believe the answer is:
local derby
'event in sheffield say' is the definition.
(Sheffield United vs Sheffield Wednesday derby)
'see yorkshire river beside' is the wordplay.
'see' becomes 'lo' (archaic word meaning 'look!').
'yorkshire river' becomes 'calder' (River Calder in West Yorkshire).
'beside' becomes 'by'.
'lo'+'calder'+'by'='LOCAL DERBY'
(Other definitions for local derby that I've seen before include "big match" , "Meeting of neighbours" , "Nearby game?" , "Match between nearby teams" , "Competition between two close teams" .)