Left-winger for soccer team in smart arrangement (7)
I believe the answer is:
marxist
'left-winger' is the definition.
(Marxist is an example)
'soccer team in smart arrangement' is the wordplay.
'soccer team' becomes 'XI' (a football team, from Roman numerals for 11).
'in' is an insertion indicator.
'arrangement' is an anagram indicator.
'smart' anagrammed gives 'marst'.
'xi' inserted within 'marst' is 'MARXIST'.
'for' is the link.
(Other definitions for marxist that I've seen before include "A leftie once" , "left-wing" , "left-winger" , "Type of communist" , "Revolutionary" .)