Sporting fixture on river is level (4)
I believe the answer is:
tier
'is level' is the definition.
(I know that level can be written as tier)
'sporting fixture on river' is the wordplay.
'sporting fixture' becomes 'tie' (a tie is a sports match).
'on' is a charade indicator (letters next to each other).
'river' becomes 'r' (abbreviation for river).
'tie'+'r'='TIER'
(Other definitions for tier that I've seen before include "Rite for a rank" , "He might do sailor's knots" , "Level of a structure" , "Bank - row" , "One securing" .)