Smacked star keeping tense so far (8)
I believe the answer is:
hitherto
'so far' is the definition.
(I know that so far can be written as hitherto)
'smacked star keeping tense' is the wordplay.
'smacked' becomes 'hit'.
'star' becomes 'hero' (both can mean a main character).
'keeping' means one lot of letters goes inside another.
'tense' becomes 't' (abbreviation used in many dictionaries).
'hero' placed around 't' is 'herto'.
'hit'+'herto'='HITHERTO'
(Other definitions for hitherto that I've seen before include "Up to this time" , "Up to this point" , "Previously" , "Up till now" , "Heretofore (8" .)