I'm playing Borg: 51-0? What a mess! (9)
I believe the answer is:
imbroglio
'what a mess' is the definition.
(I've seen this before)
'i'm playing borg 51-0?' is the wordplay.
'playing' indicates anagramming the letters.
'51' becomes 'li' (Roman numerals).
'0?' becomes 'o' (I've seen this in other clues).
'borg' with letters rearranged gives 'brog'.
'im'+'brog'+'li'+'o'='IMBROGLIO'
(Other definitions for imbroglio that I've seen before include "Confused and tangled situation" , "Jumble" , "Confused situation results" , "massive jam" , "Complicated situation" .)