Outstanding success in strike after strike (5,3)
I believe the answer is:
smash hit
'outstanding success' is the definition.
(eg a hit record)
'strike after strike' is the wordplay.
'strike' becomes 'smash' (synonyms).
'after' is a charade indicator (letters next to each other).
'strike' becomes 'hit' (synonyms).
'smash'+'hit'='SMASH-HIT'
'in' acts as a link.
(Other definitions for smash hit that I've seen before include "Really successful song" , "Major success" , "roaring success" , "Great success" , "most popular show!" .)