Line held by defender, a player in game (5)
I believe the answer is:
black
'a player in game' is the definition.
Both the definition and answer are adjectives. Maybe they are linked in a way I don't understand?
'line held by defender' is the wordplay.
'line' becomes 'l'.
'held by' means one lot of letters goes inside another.
'defender' becomes 'back' (I've seen this before).
'l' put into 'back' is 'BLACK'.
Can you help me to learn more?
(Other definitions for black that I've seen before include "Colour of jet" , "Gloomy" , "Boycott" , "Unofficial" , "Opponent of nineteen dn (chess)" .)