An all-round score? (3)
I believe the answer is:
nil
'score?' is the definition.
(I've seen this before)
'an all-round' is the wordplay.
'an' becomes 'i' (Roman numeral for one).
'all' becomes 'nl' (I can't explain this - if you can you should believe this answer much more).
'round' indicates putting letters inside.
'i' inserted into 'nl' is 'NIL'.
Can you help me to learn more?
(Other definitions for nil that I've seen before include "Nix, nada, nothing" , "Don't despair - . . . desperandum" , "Nothing - in Latin" , "Latin zero" , "You get nothing" .)