Stir up is in view they say (6)
I believe the answer is:
incite
'stir up' is the definition.
(I know that stir up can be written as incite)
'in view they say' is the wordplay.
'in view' becomes 'in sight' (synonyms).
'they say' shows a homophone (sound like).
'insight' is a homophone of 'INCITE'.
'is' acts as a link.
(Other definitions for incite that I've seen before include "Foment, urge on" , "Urge, instigate" , "Egg on" , "'Stir up, provoke (6)'" , "Encourage or stir up" .)