To slip up 1-0 to us is wrong (9)
I believe the answer is:
erroneous
'is wrong' is the definition.
(similar in meaning)
'to slip up 1-0 to us' is the wordplay.
'to slip up' becomes 'err' (to err is to make an error).
'1-0' becomes 'one o' (O resembles zero).
'err'+'oneo'+'us'='ERRONEOUS'
(Other definitions for erroneous that I've seen before include "Incorrect, wrong" , "Mistaken, in error" , "not right" , "Mistaken - inaccurate" , "with mistakes" .)