Failure of Super League? Football fans to finally riot (5)
I believe the answer is:
loser
'failure' is the definition.
(someone who has failed)
'super league? football fans to finally riot' is the wordplay.
'finally' indicates one should take the final letters.
'riot' indicates anagramming the letters.
The last letters of 'super league football fans to' are 'relso'.
'relso' is an anagram of 'LOSER'.
'of' is the link.
(Other definitions for loser that I've seen before include "Defeated person" , "Someone who fails consistently" , "One frequently failing" , "Washout" , "Generally inept" .)