Leading score is excellent (3-5)
I believe the answer is:
top-notch
'excellent' is the definition.
(I've seen this before)
'leading score' is the subsidiary indication.
'leading' becomes 'top'.
'score' becomes 'notch' (I've seen this before**).
'top'+'notch'='topnotch'
'is' is the link.
(Other definitions for top-notch that I've seen before include "Superb" , "First-rate" , "Excellent (informal)" , "Grade 1" , "Of the highest quality" .)