A disturbance when not starting sale (7)
I believe the answer is:
auction
'sale' is the definition.
(I've seen this before)
'a disturbance when not starting' is the wordplay.
'disturbance' becomes 'ruction' (ruction is a kind of disturbance).
'when not starting' means to remove the first letter.
'ruction' with its initial letter removed is 'uction'.
'a'+'uction'='AUCTION'
(Other definitions for auction that I've seen before include "event with lots involved" , "Use caution at public sale" , "Where things are sold to the highest bidder" , "Occasion of lots under the gavel" , "Selling" .)