Fanatic of foul tradition (5)
I believe the answer is:
ultra
'fanatic' is the definition.
(I've seen this in another clue)
'of foul tradition' is the wordplay.
'of' indicates a hidden word.
'ULTRA' is hidden in the letters of 'foul tradition'.
(Other definitions for ultra that I've seen before include "Extremely; an extremist" , "(One who is) extreme (in eg political opinion)" , "Prefix meaning beyond or extremely" , "(As prefix) beyond or extreme" , "Over the top" .)