Narcissist's failing badly in a game to hold onto ball (8)
I believe the answer is:
egomania
'narcissist's failing' is the definition.
(narcissists are egomaniacs)
'badly in a game to hold onto ball' is the wordplay.
'badly' indicates anagramming the letters (letters in the wrong order).
'to hold onto' means one lot of letters goes inside another.
'ball' becomes 'o' (O looks like a ball).
'in'+'a'+'game'='inagame'
'inagame' anagrammed gives 'egmania'.
'egmania' placed around 'o' is 'EGOMANIA'.
(Other definitions for egomania that I've seen before include "Abnormally excessive opinion of oneself, quite mad" , "Obsessive self-concern" , "obsession with self" , "Obsessive self-absorption" , "having no thought for others" .)