Leading score, first-rate (3-5)
I believe the answer is:
top-notch
'first-rate' is the definition.
(thesaurus)
'leading score' is the wordplay.
'leading' becomes 'top' (both can mean first-class).
'score' becomes 'notch' (I've seen this in another clue).
'top'+'notch'='TOP-NOTCH'
(Other definitions for top-notch that I've seen before include "First-rate" , "Excellent (informal)" , "Of the highest quality" , "Wonderful" , "Superb" .)