Ending in no score to poor game (5)
I believe the answer is:
omega
'ending' is the definition.
(I know that omega is a type of ending)
'no score to poor game' is the wordplay.
'no score' becomes 'o' (O resembles 0, as in a score of zero).
'to poor' indicates anagramming the letters.
'game' anagrammed gives 'mega'.
'o'+'mega'='OMEGA'
'in' is the link.
(Other definitions for omega that I've seen before include "Ending of a series or sequence" , "Greek finalist" , "Last (Gk. letter)" , "24th Greek letter" , ""The Alpha and the ___"" .)