Aggressive speech by playwright carrying a fake gun (8)
I believe the answer is:
harangue
'aggressive speech' is the definition.
(I've seen this before)
'playwright carrying a fake gun' is the wordplay.
'playwright' becomes 'Hare' (playwright David Hare).
'carrying' is an insertion indicator.
'fake' is an anagram indicator (I've seen this in other clues).
'gun' is an anagram of 'ngu'.
'a'+'ngu'='angu'
'hare' placed around 'angu' is 'HARANGUE'.
'by' is the link.
(Other definitions for harangue that I've seen before include "Declamation - lecture" , "A lengthy earnest speech" , "Long, loud and aggressive speech" , "Exhortation" , "A lengthy speech or scolding" .)