Niceness enough to start riot, basically (2,7)
I believe the answer is:
in essence
'basically' is the definition.
('in essence' can be a synonym of 'basically')
'niceness enough to start riot' is the wordplay.
'to start' suggests taking the first letters.
'riot' indicates anagramming the letters.
The initial letter of 'enough' is 'e'.
'niceness'+'e'='nicenesse'
'nicenesse' anagrammed gives 'IN ESSENCE'.
(Other definitions for in essence that I've seen before include "Substantially" , "Fundamentally" , "Basically" , "at bottom" .)