Away team in illegal position (7)
I believe the answer is:
offside
'illegal position' is the definition.
(I've seen this before)
'away team' is the wordplay.
'away' becomes 'off' (synonyms).
'team' becomes 'side' (both can mean a sports team).
'off'+'side'='OFFSIDE'
'in' acts as a link.
(Other definitions for offside that I've seen before include "Illegal football position between the ball and opponents' goal" , "Illegal state in football" , "in no position to score goal" , "Part of vehicle furthest from kerb" , "Illegal position on soccer field" .)