Player in game, fly-half possibly, crossing line (5)

I believe the answer is:
black
'player in game' is the definition.
The definition and answer can be both people as well as being singular nouns.
Maybe they are linked in a way I don't understand?
'fly-half possibly crossing line' is the wordplay.
'fly half possibly' becomes 'back' (I am not sure about this - if you are sure you should believe this answer much more).
'crossing' is an insertion indicator (to cross can mean to go over or around).
'line' becomes 'l' (used when specifying particular lines from a poem).
'back' placed around 'l' is 'BLACK'.
Can you help me to learn more?
(Other definitions for black that I've seen before include "It produces illegally undeclared income" , "Uncommon H [HORSE]" , "Colour of jet" , "bar" , "(Of coffee) without milk" .)
