What supporter has in street, playing with ball (7)
I believe the answer is:
rosette
'what supporter has' is the definition.
(supporters might wear rosettes)
'street playing with ball' is the wordplay.
'playing with' indicates an anagram.
'ball' becomes 'o' (O looks like a ball).
'street' mixed up with 'o' can make 'ROSETTE'.
'in' acts as a link.
(Other definitions for rosette that I've seen before include "Ribbon decoration" , "Colourful decoration worn by supporters" , "Arrangement of ribbons presented as a prize" , "collection of ribbons" , "decoration showing support for party" .)