Pigeon supporter has to follow (7)
I believe the answer is:
fantail
'pigeon' is the definition.
(type of pigeon)
'supporter has to follow' is the wordplay.
'supporter' becomes 'fan' (fan is a kind of supporter).
'has' says to put letters next to each other.
'to follow' becomes 'tail' (both can mean to chase or pursue).
'fan'+'tail'='FANTAIL'
(Other definitions for fantail that I've seen before include "Flier" , "Bird" , "Variety of pigeon" , "Type of domestic pigeon" , "In a flat (anag.)" .)