All the players losing could get one depressed (4,4)
I believe the answer is:
cast down
'one depressed' is the definition.
(I've seen this before)
'all the players losing' is the wordplay.
'all the players' becomes 'cast' (I've seen this before).
'losing' becomes 'down' (similar in meaning).
'cast'+'down'='CAST DOWN'
'could get' acts as a link.
(Other definitions for cast down that I've seen before include "Discouraged" , "Dishearten" , "in need of encouragement" , "Gloomy" , "disheartened" .)