Comedian senses upset viewers (9)
I believe the answer is:
witnesses
'viewers' is the definition.
('witness' can be a synonym of 'viewer')
'comedian senses upset' is the wordplay.
'comedian' becomes 'wit' (a witty person).
'upset' indicates an anagram.
'senses' with letters rearranged gives 'nesses'.
'wit'+'nesses'='WITNESSES'
(Other definitions for witnesses that I've seen before include "They testify under oath in a court of law" , "They provide sworn testimony" , "Sees" , "Observers" .)