Passed in City's second half score (6)
I believe the answer is:
twenty
'score' is the definition.
(synonyms)
'passed in city's second half' is the wordplay.
'passed' becomes 'went' (I've seen this in other clues).
'in' is an insertion indicator.
'second half' indicates taking half.
'city' halved is 'ty'.
'went' going inside 'ty' is 'TWENTY'.
(Other definitions for twenty that I've seen before include "Score, XX" , "John B Keane wrote about many young men of this age" , "Hundredweights to a ton" , "Number" , "with two crosses" .)