Make better, mostly unscripted performance (6)
I believe the answer is:
improv
'unscripted performance' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'make better mostly' is the wordplay.
'make better' becomes 'improve' (synonyms).
'mostly' means to remove the last letter (most but not all of the word).
'improve' with its last letter taken away is 'IMPROV'.
Can you help me to learn more?
(Other definitions for improv that I've seen before include "little ad-libbing" , "Off-the-cuff comedy" , "Stand-up comedy, perhaps" , "off-the-cuff humour" .)