Disturbance about a large sort of triangle (7)
I believe the answer is:
scalene
'sort of triangle' is the definition.
'disturbance about a large' is the wordplay.
'disturbance' becomes 'scene' (I've seen this in another clue).
'about' indicates putting letters inside.
'large' becomes 'L' (eg in clothes sizes).
'a'+'l'='al'
'scene' placed around 'al' is 'SCALENE'.
(Other definitions for scalene that I've seen before include "not having evenly matched sides" , "(Of triangle) with each side of a different length" , "Neither equilateral nor isosceles" , "(Of triangle) with no sides equal" , "(Of triangle) having three unequal sides" .)